No one has produced the winning EuroMillions Millionaire Raffle ticket which was bought in South Lanarkshire on November 4.
Organisers of the raffle, which makes two millionaires a week, are urging players to check their tickets for the chance to claim the money.
The draw in question took place the day before Bonfire Night and officials say the winner may have bought a ticket before or after attending a fireworks display.
A National Lottery spokesperson said: “We’re desperate to find this mystery ticket holder and unite them with their winnings. This amazing prize could really make a huge difference to somebody’s life.
“Being able to guarantee two UK millionaires every week with Millionaire Raffle is fantastic, and we’re urging everyone to check their old EuroMillions tickets again or look anywhere a missing ticket could be hiding so that this prize can turn someone into the newest member of the lottery millionaire club.
“Try checking in the pockets of clothing, in wallets, bags and down the back of the sofa. We have the champagne on ice and our fingers crossed that the lucky winner comes forward to claim their win.”
For every EuroMillions line played, UK players automatically receive a Millionaire Raffle selection printed on their ticket.
The winning selection on Friday November 4 was NSX597128. The ticket holder has until May 2 next year to make the claim.
Another 13 Lottery and EuroMillions prizes are currently unclaimed in the UK.
National Lottery said the money goes to good causes if no one produces a winning ticket before the prize claim deadlines.