The middle-aged man, from the English county of Surrey near London, placed the bet at odds of 1/4, meaning he stands to make a profit of 100,000 pounds if Scotland votes to stay in the United Kingdom on September 18.
"As far as we can ascertain, this is the biggest political bet ever struck," said Graham Sharpe, a spokesman for national bookmaker William Hill, which took the wager at one of its London branches.
The previous record for a political wager was a 200,000 pounds bet, also laid on a "No" vote but earlier in the campaign, the bookmaker said.
The latest polling data compiled by the Financial Times found 48 per cent of Scotland's four million voters are against independence, compared to 35 per cent in favour. Some 16 percent remain undecided.
