Sir Paul McCartney has added his weight to a campaign against Scottish independence.

The Beatles legend has signed an open letter to voters in the country urging them to choose 'No' in a crucial poll over plans for the nation to break away from the rest of the U.K.

MCCartney, who penned his classic track Mull of Kintyre in honour of his beloved estate in Scotland, has added his name to the notice, which states: "We want to let you know how very much we value our bonds of citizenship with you, and to express our hope that you will vote to renew them... What unites us is much greater than what divides us. Let's stay together."

Other stars who have already signed it include Sir Mick Jagger, Michael Douglas, Sting, and Dame Judi Dench, while singer Morrissey and funnyman Russell Brand are backing the independence campaign.

Tv historian Dan Snow is adamant MCCartney's support is a major boost to the 'No' campaign, saying, "Sir Paul is one of the world's most respected musicians. We are humbled that he has signed the letter.

"Sir Paul's signature, alongside Sir Mick Jagger's and those of tens of thousands of people from all over the country, shows that English, Welsh and Northern Irish people hope passionately that the Scottish vote to renew their bonds of citizenship with us."

Scotland goes to the polls on the issue in September (14).