A Glasgow punter scooped more than £350,000 - from a £1 seven-horse accumulator bet.
Bookies William Hill said the man, who wishes to stay anonymous, scooped £353,000, reports the Daily Telegraph.
The single father has not worked in five years after he had surgery on his heart, and admitted he was struggling.
He said: "I'm shocked. I regularly place these little bets and everyone tells me I'm mad. I've hit the bar a few times but this is incredible.
"My brain was a wreck and I couldn't understand the balance on my account.
"I first thought it would pay about £21,000 and had to get my son to come and translate that the numbers meant I'd actually won £353,000."
He said he would spend his winnings on buying his own home, and planned to visit his sisters abroad.
He placed his 50p each-way accumulator on seven horses running at Brighton, Nottingham, Towcester and Kempton.
A spokesman for William Hill said: "He's our luckiest ever punter."