A couple who won £161 million on the EuroMillions lottery have given another £1 million to the SNP, taking their total contribution to Scottish independence campaigners to £5.5 million.

Chris and Colin Weir donated £500,000 each to the Scottish National Party on February 10, the Electoral Commission's register of donations for the first three months of this year has revealed.

It comes on top of another £1 million they donated to the SNP in September 2011, and the £3.5 million they have donated to the Yes Scotland campaign in the last two years.

The UK Conservative Party received £6,662,232, the register shows, with over a fifth from a single donor - British-Australian hedge fund boss Sir Michael Hintze who donated £1,506,500.

Labour received £4,409,167 with two-thirds of it coming from the unions Unite, Usdaw and Unison, while the Liberal Democrats received £1,074,482.

An SNP spokeswoman said: "We thank all of our donors - big and small - for contributing to the success of the party, including consistently being ahead in the polls after eight years in government, which is a remarkable achievement.

"The SNP has never been in better shape - with a record membership of over 25,000 - and we are fighting fit to help achieve the Yes vote in September which is so important to Scotland's future."

Labour constitutional spokesman Drew Smith said: "The Weirs are entirely entitled to spend their lottery winnings as they wish but the revelation that the SNP and the Yes campaign are relying on just one family for their funding does rather undermine the Nationalists' claims of a broad-based grassroots campaign."

Scottish Conservative chief whip John Lamont said: "The SNP is clearly embarrassed that such an overwhelming proportion of its funding is coming from one source.

"It also renders a nonsense claims that it and the Yes campaign are popular, grassroots movements.

"The fact is, if the Weirs hadn't picked their lucky numbers, the independence movement would be millions of pounds worse off."