Bookies at Ladbrokes were stunned to see a first-time better stroll into the firm's Marble Arch branch and put £35,000 — in cash — on a vote to Remain on Thursday.
With odds of an "In" vote now at 4/7, the unnamed cash-buyer could take home £55,000 next week.
Meanwhile in Mayfair, another well-heeled money buyer has bought a £10,000 stake on Britain staying in the EU after 23 June, and the betmaker says he's never been wrong before.
Bookies say the punter is "rarely seen in the shop", but every so often will come in to place a five-figure sum on what he believes to be an absolute certainty -- and he's got a good track record.
The last two bets the Mayfair gent placed included an £14,000 stake on Djokovic beating Murray in the final of the French open earlier this month, and £7,000 on New Zealand beating Australia in the rugby world cup final last year. These sure bets won the punter £18,000 and £9,000 respectively.
If successful, the gambler could pick up over £15,700 in profit on 24 June.