National Lottery officials are desperately searching for a lucky winner who has still not claimed a £1m prize, Camelot said today.
The owner of the winning EuroMillions Millionaire Raffle selection bought their ticket in the York area of North Yorkshire, for the New Year's Day draw.
A spokesman for the National Lottery urged anyone who bought a EuroMillions ticket in the area to check it and, if they find it is the winner, to come forward before the 180-day deadline expires.
"We're desperate to find this mystery ticket-holder and unite them with their winnings," the spokesman said. "This amazing prize could really make a huge difference to somebody's life.
"Being able to guarantee a UK millionaire 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 give someone a really great start to 2010.
"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."
Millionaire Raffle is the newest game from the National Lottery, where for every EuroMillions line played, UK players automatically receive a Millionaire Raffle selection printed on their EuroMillions ticket.
The winning Millionaire Raffle selection on January 1 was SDV403955 and the ticket-holder has until 5.30pm on June 30 to make their claim.
If no one comes forward with the winning ticket before the prize claim deadline, then the prize money, plus all the interest it has generated, will go to the Good Causes - adding to the £24bn already raised through sales of lottery tickets since The National Lottery launched in November 1994.