The Shard building and the Canary Wharf financial district are seen from the Broadway development in central London, Britain, August 23, 2017. Picture taken August 23, 2017. REUTERS/Hannah McKay

The top of the Shard building, illuminated to resemble a Christmas tree, is seen behind the Tower of London in London, Britain, December 11, 2017. Picture taken December 11, 2017. REUTERS/Clodagh Kilcoyne

The top of the Shard building, illuminated to resemble a Christmas tree, is seen behind the Tower of London in London, Britain, December 11, 2017. Picture taken December 11, 2017. REUTERS/Clodagh Kilcoyne

The top of the Shard building, illuminated to resemble a Christmas tree, is seen behind the Tower of London in London, Britain, December 11, 2017. Picture taken December 11, 2017. REUTERS/Clodagh Kilcoyne

The Shard building is seen through the Tower of London in London, Britain July 20, 2017. Picture taken July 20, 2017.REUTERS/Neil Hall

The Shard building is silhouetted during sunrise in central London, Britain December 29, 2016. REUTERS/Stefan Wermuth

The Shard building is silhouetted during sunrise in central London, Britain December 29, 2016. REUTERS/Stefan Wermuth

The Shard building is silhouetted during sunrise in central London, Britain December 29, 2016. REUTERS/Stefan Wermuth

An aircraft flies past the Shard building during sunrise in London, Britain December 29, 2016. REUTERS/Stefan Wermuth

An aircraft flies past the Shard building during sunrise in London, Britain December 29, 2016. REUTERS/Stefan Wermuth

The Shard building catches the early evening light as tourists cross the Millennium Bridge in London, Britain December 4, 2016. REUTERS/Peter Nicholls

Fog surrounds the Shard building in London, Britain October 31, 2016. REUTERS/Stefan Wermuth

Fog surrounds the Shard building in London, Britain October 31, 2016. REUTERS/Stefan Wermuth

Fog surrounds the Shard building in London, Britain October 31, 2016. REUTERS/Stefan Wermuth

A man looks at a view of The Shard building in London, Britain October 3, 2016. REUTERS/Neil Hall

The shadow of western Europe's tallest building, the Shard, is cast across the financial district as seen from it's The View gallery in London January 9, 2013. REUTERS/Luke Macgregor/File Photo

The shadow of western Europe's tallest building, the Shard, is cast across the financial district as seen from it's The View gallery in London January 9, 2013. REUTERS/Luke Macgregor/File Photo GLOBAL BUSINESS WEEK AHEAD PACKAGE - SEARCH 'BUSINESS WEEK AHEAD MAY 16' FOR ALL IMAGES

Athletics - 2016 Virgin Money London Marathon - London - 24/4/16
General view of the Shard building during the marathon
Reuters / Toby Melville
Livepic
EDITORIAL USE ONLY.

Athletics - 2016 Virgin Money London Marathon - London - 24/4/16
General view of the Shard building during the marathon
Reuters / Toby Melville
Livepic
EDITORIAL USE ONLY.

The Shard skyscraper is seen at sunrise from the Sky Garden of 20 Fenchurch Street, nicknamed the Walkie-Talkie building, in the financial district of the City of London, February 19, 2016. REUTERS/Eddie Keogh

A red bus passes in front of St Paul's Cathedral and the Shard building in London, Britain January 24, 2016. The City of London financial district is home to a variety of banks and financial instiutions. REUTERS/Neil Hall

The Shard building and London Eye are seen at dawn in central London, Britain January 19, 2016. REUTERS/Toby Melville

The Shard building is silhouetted during sunrise in central London, Britain January 14, 2016. REUTERS/Stefan Wermuth

The sun is seen through a window of the Shard building during sunrise in central London, Britain January 14, 2016. REUTERS/Stefan Wermuth TPX IMAGES OF THE DAY

A runner passes a view of the Shard building on the shore of the River Thames on a sunny day in London, Britain December 28, 2015. REUTERS/Neil Hall

The spire of St. Magnus the Martyr church (C) is dwarfed by The Shard skyscraper in the City of London business district, Britain November 2, 2015. The architectural landscape of London never stands still. The City of London, as the largest financial services and banking centre in Europe, is no exception. Silhouettes of cranes pepper the horizon and buildings shoot skywards. Amid all this change there appears to be one constant: over 50 churches and other places of worship remain in the Square Mile. REUTERS/Toby Melville PICTURE 1 OF 15 - SEARCH "MELVILLE WORSHIP" FOR ALL IMAGES TPX IMAGES OF THE DAY

The Shard and Tower Bridge are seen amongst other buildings in London November 3, 2015. REUTERS/Kevin Coombs

Fog is seen clearing around the Shard skyscraper in London, Britain, November 2, 2015. Airports across Britain suffered disruption on Monday as heavy fog led to delays and cancellations for a second day. Flights to and from London airports were being affected, while foggy conditions in the capital and across Europe were causing problems to airports around the country. REUTERS/Toby Melville

Fog is seen clearing around the Shard skyscraper in London, Britain, November 2, 2015. Airports across Britain suffered disruption on Monday as heavy fog led to delays and cancellations for a second day. Flights to and from London airports were being affected, while foggy conditions in the capital and across Europe were causing problems to airports around the country. REUTERS/Toby Melville

Fog is seen clearing around the Shard skyscraper in London, Britain, November 2, 2015. Airports across Britain suffered disruption on Monday as heavy fog led to delays and cancellations for a second day. Flights to and from London airports were being affected, while foggy conditions in the capital and across Europe were causing problems to airports around the country. REUTERS/Toby Melville

The Shard building is seen through electricity cables in London October 3, 2015. REUTERS/Kevin Coombs

The Shard skyscraper is seen on the skyline of London, September 3, 2015. REUTERS/Toby Melville

Sunlight illuminates the Canary Wharf district, behind the Shard building in London, Britain September 2, 2015. Photograph taken September 2, 2015. REUTERS/Eddie Keogh

The Shard building is seen in front of dark clouds in central London, Britain September 2, 2015. Photograph taken September 2, 2015. REUTERS/Eddie Keogh

A rainbow is seen over the Shard building in central London, Britain September 2, 2015. Photograph taken September 2, 2015. REUTERS/Eddie Keogh

A window cleaner works outside on the 69th floor of the Shard building in London, Britain June 22, 2015. REUTERS/Stefan Wermuth

A window cleaner works outside on the 69th floor of the Shard building in London, Britain June 22, 2015. REUTERS/Stefan Wermuth

Window cleaners work outside on the 69th floor of the Shard building in London, Britain June 22, 2015. REUTERS/Stefan Wermuth

A window cleaner works outside on the 72th floor of the Shard building in London, Britain June 22, 2015. REUTERS/Stefan Wermuth

A window cleaner works outside on the 72th floor of the Shard building in London, Britain June 22, 2015. REUTERS/Stefan Wermuth

A sign with the Takata logo is seen on the building of the Takata Corporation in Auburn Hills, Michigan May 20, 2015. Takata Corp said on Wednesday it plans to boost production of parts needed to replace potentially deadly air bag inflators that could spray vehicle occupants with metal shards. On Tuesday, the Japanese supplier doubled its recall of the defective air bags to nearly 34 million vehicles, making it the largest automotive recall in U.S. history. REUTERS/Rebecca Cook

A sign with the Takata logo is seen along the driveway leading to the Takata Corporation building in Auburn Hills, Michigan May 20, 2015. Takata Corp said on Wednesday it plans to boost production of parts needed to replace potentially deadly air bag inflators that could spray vehicle occupants with metal shards. On Tuesday, the Japanese supplier doubled its recall of the defective air bags to nearly 34 million vehicles, making it the largest automotive recall in U.S. history. REUTERS/Rebecca Cook

A sign with the TAKATA logo is seen outside the Takata Corporation building in Auburn Hills, Michigan May 20, 2015. Takata Corp said on Wednesday it plans to boost production of parts needed to replace potentially deadly air bag inflators that could spray vehicle occupants with metal shards. On Tuesday, the Japanese supplier doubled its recall of the defective air bags to nearly 34 million vehicles, making it the largest automotive recall in U.S. history. REUTERS/Rebecca Cook

City workers are reflected in a window as they pass near the Shard building in London, Britain April 28, 2015. Britain's economy slowed more sharply than expected the first three months of 2015 in a setback for Prime Minister David Cameron who has staked his campaign for re-election next week on the strength of the recovery. REUTERS/Neil Hall

The sun is reflected off The Shard in London January 30, 2015. REUTERS/Eddie Keogh (BRITAIN - Tags: BUSINESS EMPLOYMENT CITYSCAPE)

The Shard is seen behind some old brick buildings in London January 30, 2015. REUTERS/Eddie Keogh (BRITAIN - Tags: BUSINESS EMPLOYMENT CITYSCAPE)

The full moon rises behind the Shard building in London December 5, 2014. REUTERS/Andrew Winning (BRITAIN - Tags: CITYSCAPE ENVIRONMENT)

The full moon rises behind the Shard building in London December 5, 2014. REUTERS/Andrew Winning (BRITAIN - Tags: CITYSCAPE ENVIRONMENT)

The full moon rises behind the Shard building in London December 5, 2014. REUTERS/Andrew Winning (BRITAIN - Tags: CITYSCAPE ENVIRONMENT TPX IMAGES OF THE DAY)

The shadow of The Shard, western Europe's tallest building, is cast over buildings lining the river Thames in London October 27, 2014. Picture taken from The View From the Shard. REUTERS/Suzanne Plunkett (BRITAIN - Tags: CITYSCAPE SOCIETY)

Wembley Stadium is seen from The View gallery at The Shard, western Europe's tallest building, in London October 27, 2014. REUTERS/Suzanne Plunkett (BRITAIN - Tags: CITYSCAPE SPORT)

A woman walks through shards of broken glass in front of a business damaged by Sunday's magnitude 6.0 earthquake in Napa, California August 25, 2014. The quake, the biggest to hit California's Bay area in 25 years, struck before dawn on Sunday 6 miles south of Napa, damaging dozens of buildings in the picturesque community north of San Francisco, triggering fires and disrupting water and power service to the area, but no deaths were reported. REUTERS/Robert Galbraith (UNITED STATES - Tags: DISASTER)

Competitors run past a view of the Shard building during the women's elite class runners at the London Marathon April 13, 2014. REUTERS/Neil Hall (BRITAIN - Tags: SPORT ATHLETICS)

Smog surrounds The Shard, western Europe's tallest building, and St Paul's Cathedral in London April 3, 2014. A dust cloud from the Sahara has covered south east England, raising pollution levels to the highest level in London, preventing people taking exercise outdoors, including the Prime Minister, David Cameron, who said he had skipped his morning jog. REUTERS/Suzanne Plunkett (BRITAIN - Tags: ENVIRONMENT TPX IMAGES OF THE DAY)

Smog surrounds The Shard, western Europe's tallest building, in London April 1, 2014. Britain's Meteorological Office has forecast London to be affected by smog this week, caused by powerful dust storms and strong winds in the Sahara. REUTERS/Suzanne Plunkett (BRITAIN - Tags: ENVIRONMENT CITYSCAPE)

Birds circle the Shard as it casts a shadow across the morning mist in central London, April 1, 2014. REUTERS/Andrew Winning (BRITAIN - Tags: ENVIRONMENT CITYSCAPE ANIMALS)

Shards of glass are seen next to wilted flowers outside St. Paul's Roman Catholic Church near the site of a building collapse in Harlem, New York March 12, 2014. A building collapsed in Upper Manhattan on Wednesday, killing at least one person and injuring more than a dozen, setting off a search for anyone trapped in the debris, officials said. Massive clouds of smoke billowed from the charred rubble of the structure on the largely residential block at East 116th Street and Park Avenue in East Harlem, which reportedly collapsed sometime after 9 a.m. (1300 GMT). REUTERS/Shannon Stapleton (UNITED STATES - Tags: DISASTER RELIGION)

The BT communication tower is seen from The View gallery at the Shard, western Europe's tallest building, in London January 28, 2014. Britain's BT returned to quarterly revenue growth for the first time in four and a half years on January 31, 2014, driven by record customer demand for superfast broadband and its growing new sports TV service.The 168-year-old former state telecoms monopoly, which last reported revenue growth shortly before a major profit warning in the first quarter of 2009, said revenue for the three months to the end of December was up 2 percent to 4.6 billion pounds, ahead of expectations at 4.5 billion pounds. Photograph taken January 28, 2014. REUTERS/Suzanne Plunkett (BRITAIN - Tags: BUSINESS TELECOMS)

Wembley Stadium is seen from The View gallery at the Shard, western Europe's tallest building, in London January 28, 2014. Britain's economy grew last year at its fastest rate since the financial crisis, official data showed on Tuesday, raising questions about how long the Bank of England can keep interest rates at a record low. REUTERS/Suzanne Plunkett (BRITAIN - Tags: BUSINESS)

Buildings in the Canary Wharf business district are seen from The View gallery at the Shard, western Europe's tallest building, in London January 28, 2014. Britain's economy grew last year at its fastest rate since the financial crisis, official data showed on Tuesday, raising questions about how long the Bank of England can keep interest rates at a record low. REUTERS/Suzanne Plunkett (BRITAIN - Tags: BUSINESS)