Two £1 million EuroMillions raffle prizes have not yet been claimed, Camelot said.
The EuroMillions Millionaire Raffle winners, who bought their tickets in Nottingham and Doncaster last month, have until September to claim their prize money.
If no one comes forward, the money will be added to the National Lottery Good Causes fund, which has raised £27 billion since 1994.
A National Lottery spokesman said: “The clock is now ticking for these two lucky ticket-holders.
“Anyone who played EuroMillions in these areas should check their tickets as they could now be worth £1 million.
“We want players to check down the back of the sofa and in coat pockets as these millions could be hiding anywhere.”
The raffle is a UK-only game that is part of the EuroMillions ticket. It guarantees to create a UK millionaire every Tuesday and Friday.
Anyone who matches the unique Millionaire Raffle number at the bottom of their ticket wins £1 million.
The Nottingham ticket - selection LHZ360128 - won in the March 23 draw, while the Doncaster ticket - selection FGL789613 - won on March 27.