A £500,000 National Lottery Thunderball prize is yet to be claimed from a ticket bought in Islington.
The ticket won the top prize in a draw on June 1 but is still unclaimed.
Lottery players are being asked to check their tickets as the search to find the lucky winner gets underway.
The winning Thunderball numbers on the draw date were 09, 21, 31, 35, 36, and the Thunderball was 9.
The ticket-holder who matched all five main numbers and the Thunderball has until November 28 to claim the half a million-pound prize.
Even those without their ticket but who believe they have a legitimate claim may still appeal, but it must be in writing to The National Lottery within 30 days of the draw.
Andy Carter, senior winners’ advisor at The National Lottery, said: "If you bought a Thunderball ticket in Islington for the draw on Saturday 1 June, it's time to look everywhere.
"In the pockets of clothes you might have been wearing at the time, bags, wallets and purses or in the car or that sideboard or drawer where we all tend to put all our bits and pieces.
"Find that ticket and check it!"
Mr Carter added: "We're desperate to find this mystery ticket-holder and pay out their life-changing prize.
"We have the champagne on ice and our fingers crossed that the lucky winner comes forward to claim their win."
The tickets can be checked online by downloading the National Lottery app or at national-lottery.co.uk.
Players can also check if they have won in shops that sell National Lottery tickets.
If the prize remains unclaimed by the deadline, the prize money, along with any interest it has generated, will be allocated to National Lottery-funded projects across the UK.
Each week, National Lottery games generate £30 million supporting more than 690,000 projects nationwide.
The National Lottery allows winners of any draws 180 days from the day of the draw to claim their prize.
For queries or claims, they can call the National Lottery Line on 0333 234 5050 or email help@national-lottery.co.uk.
Those worried about lost or unchecked tickets might prefer to set up a National Lottery Direct Debit or play online at www.national-lottery.co.uk.
In this way, the numbers can be entered in advance and winners are notified online.
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