Scotland's First Minister Nichola Sturgeon smiles as she arrives with Britain's Queen Elizabeth (not shown) at Newtongrange railway station, in Scotland, September 9, 2015. Queen Elizabeth officialy opened the new Scottish Borders Railway on the day she became Britain's longest reigning monarch. REUTERS/Andrew Milligan/Pool 

Britain's Queen Elizabeth travels with Prince Philip and Scotland's First Minister Nichola Sturgeon (L) on the new Scottish Borders railway line, in Scotland, September 9, 2015. Queen Elizabeth officialy opened the new Scottish Borders Railway on the day she became Britain's longest reigning monarch. REUTERS/Andrew Milligan/Pool 

Britain's Queen Elizabeth travels with Prince Philip and Scotland's First Minister Nichola Sturgeon (L) on the new Scottish Borders railway line, in Scotland, September 9, 2015. Queen Elizabeth officialy opened the new Scottish Borders Railway on the day she became Britain's longest reigning monarch. REUTERS/Andrew Milligan/Pool 

Scotland's First Minister Nicola Sturgeon steps out of the cab of steam locomotive Union of South Africa at Waverley station in Edinburgh, Scotland, September 9, 2015. Sturgeon joined Britain's Queen Elizabeth as she travelled on the train to officially open the Scottish Borders Railway on the day she became Britain's longest reigning monarch. REUTERS/Andrew Milligan/Pool 

Britain's Prime Minister Gordon Brown (R) and his spokesperson Iain Bundred return by train from Southampton to London, April 26, 2010. Britain's opposition Conservatives launched a new drive on Monday to dislodge the ruling Labour Party from some of its strongholds and talked up the risk of an inconclusive May 6 election result. The centre-right Conservatives are battling to oust centre-left Labour from government after 13 years. Both parties face a surprise challenge from the centrist Liberal Democrats, who have trailed in third place for years but whose popularity has surged in the last 10 days since a strong showing by their leader Nick Clegg in Britain's first televised election debates. REUTERS/Suzanne Plunkett (BRITAIN - Tags: ELECTIONS POLITICS) 

Scottish National Party leader Alex Salmond stands in front of the Fourth rail bridge at South Queensferry during election campaign May 5. The Scots tomorrow go to the polls to elect the country's first parliament for 300 years.
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Scottish National Party leader Alex Salmond (C) sits in front of the Fourth rail bridge at South Queensferry during election campaign May 5. The Scots tomorrow go to the polls to elect the country's first parliament for 300 years.
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Scottish National Party leader Alex Salmond stands in front of the Fourth rail bridge at South Queensferry during election campaign May 5. The Scots tomorrow go to the polls to elect the country's first parliament for 300 years.
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Scottish National Party leader Alex Salmond stands in front of the Fourth rail bridge at South Queensferry during election campaigning May 5. The Scots tomorrow go to the polls to elect the country's first parliament for 300 years.

JJM/JDP 

Scottish National Party leader Alex Salmond (C) sits in front of the Fourth rail bridge at South Queensferry during election campaigning May 5. The Scots tomorrow go to the polls to elect the country's first parliament for 300 years.

JJM 

Scottish National Party leader Alex Salmond stands in front of the Fourth rail bridge at South Queensferry during election campaigning May 5. The Scots tomorrow go to the polls to elect the country's first parliament for 300 years.

JJM/NS/