A world-record bet of £400,000 was placed yesterday on Scots voting against independence in September.
Bookmakers William Hill said the man was from Surrey, did not have a Scottish accent, and placed the bet in south-west London.
It was paid via banker’s draft at odds of 1/4, and the unnamed man now stands to make a profit of about £100,000 if there is a No vote in the referendum.
William Hill said it believed it was the largest political bet ever made in the world.
It doubled the previous record of £200,000, which was equalled earlier in the referendum campaign by a punter in Glasgow, in three separate bets at odds of 1/5 and 1/6.
In 2005, a gambler successfully wagered £200,000 that David Cameron would be elected leader of the Conservative Party.
William Hill believes it will now take more than £1million in bets on the outcome of the independence referendum.
It has shortened its odds for a No vote from 1/4 to 1/5, and is offering 10/3 that Scots will back independence, from 11/4.
Announcing yesterday’s record bet, company spokesman Graham Sharpe said: “As far as we can ascertain this is the biggest political bet ever struck.
“‘The previous record was a £200,000 bet also struck on a No vote in the Scottish referendum earlier in the campaign, and the same amount was gambled by a customer who backed David Cameron to become Tory Leader.
“‘We are now well on the way to turning over £1million on the outcome of the Scottish Referendum which is exceeding our expectations.”
He added that the client who made the £400,000 bet was a “middle-aged man who does not have Scottish accent”.