On the UK campaign trail

Britain's Deputy Prime Minister and Liberal Democrat Party leader Nick Clegg drops a ball as he plays a game of mini tennis with local children during a campaign event in Solihull, Britain, May 5, 2015. REUTERS/Darren Staples

Britain's Chancellor of the Exchequer George Osborne works on a component during a visit to a generator manufacturer in Leeds, Britain, May 5, 2015. Britain will go to the polls in a national election on May 7. REUTERS/Phil Noble

Nicola Sturgeon (R), leader of the Scottish National Party, sits at a table during an election visit to the ABC Nursery in Livingston, Britain May 5, 2015. REUTERS/Russell Cheyne

Leader of the Scottish National Party Nicola Sturgeon poses for a photograph outside Nardini's ice cream parlour and cafe, Largs, Scotland, May 4, 2015. REUTERS/Paul Hackett

Prime Minister David Cameron joins local supporters in a 'selfie' photograph in Norton Sub Hamdon near Yeovil, south west England, Britain, April 25, 2015. REUTERS/Toby Melville

Nicola Sturgeon, leader of the Scottish National Party, visits Jump Gymnastics community club during a campaign event in Cumbernauld, Scotland, April 26, 2015. REUTERS/Russell Cheyne

Nicola Sturgeon poses with local candidate Michelle Thomson during a campaign visit in South Queensferry, Britain April 28, 2015. REUTERS/Russell Cheyne

A Conservative Party activist holds a face mask of Nicola Sturgeon upside down during a stunt outside the Houses of Parliament, in central London, Britain, May 1, 2015. The Conservative Party activists were attempting to link a vote for the SNP with support for the opposition Labour Party. REUTERS/Peter Nicholls

Nicola Sturgeon poses for a photograph on a carousel at a theme park in Motherwell, central Scotland, May 3, 2015. REUTERS/Paul Hackett

David Cameron (R) and London Mayor Boris Johnson (L) react as they join a hand-printing session with children at the Advantage children's daycare nursery in Surbiton in southwest London, April 22, 2015. REUTERS/Toby Melville

Campaign placards are placed on seats, ahead of a speech by Ed Miliband on health, at a campaign event in Leeds, northern England, April 23, 2015. REUTERS/Phil Noble

A youth shouts at Nigel Farage as he visits Rochester during a campaign event, southeast England, April 20, 2015. REUTERS/Stefan Wermuth

Scottish Labour Party leader Jim Murphy campaigns at the Little Treasures Nursery in Cumbernauld, Glasgow, Scotland, April 14, 2015. REUTERS/Russell Cheyne

Nicola Sturgeon holds a baby during campaigning in Inverurie, Aberdeenshire, April 18, 2015. REUTERS/Russell Cheyne

Liberal Democrat Party leader Nick Clegg and a group of children show off their hands covered with green modelling dough at a day nursery in Poole, Britain April 27, 2015. REUTERS/Suzanne Plunkett

David Cameron and his wife Samantha take part Vaisakhi Nagar Kirtan procession at Guru Nanak Darbar Gurdwara in Gravesend, April 18, 2015. REUTERS/Peter Macdiarmid/Pool

David Cameron and his wife Samantha talks to first-time home-buyers Robert Arron (2nd R) and Kelly Jeffers (R) with their son Finlay during a general election campaign visit to a housing development in Chorley, northwest England April 3, 2015. REUTERS/Leon Neal/Pool

UKIP supporters stand near a children's toy car with a poster protesting against the HS2 rail project on Sunnyhill Farm in Martson, April 7, 2015. REUTERS/Darren Staples

David Cameron eats lunch with Lilli Docherty and her daughter Dakota in the garden with people who have benefited from tax and pension changes that came into force today, near Poole, southwest England, Monday, April 6, 2015. REUTERS/Kirsty Wigglesworth/Pool

Ed Balls leaves after making an election campaign speech at the Hilton Hotel in Leeds, April 6, 2015. REUTERS/Andrew Yates

David Cameron feeds an orphaned lamb during a visit to Dean Lane Farm near Chadlington, southern England April 5, 2015. REUTERS/Leon Neal/Pool

A young Labour supporter wears a campaign t-shirt at an election campaign event in Warrington, northwest England, April 4, 2015. REUTERS/Peter Nicholls

David Cameron talks with pupils during a general election campaign visit to the Kings Leadership Academy in Warrington, April 2, 2015. REUTERS/Leon Neal/Pool