The £40,957,696.60 prize was the seventh time the continent-wide lottery has been scooped in the UK this year.
The winning ticket-holder matched all five main numbers and the two lucky star in the draw on 3 December. The winning numbers were 18, 31, 32, 38 and 48, with lucky stars 04 and 12.
But if the winner has lost or accidentally destroyed their ticket, they have just one week left – until 2 January – to submit a claim in writing.
Operator Camelot will then determine whether the claim is valid, and would decide if it will pay out within 180 days of the draw date.
There is also a second deadline for anyone with the winning ticket still in their possession. They have until midnight on 31 May to make their claim.
Andy Carter, senior winners adviser with Camelot, said: “It’s important that any player who is not in possession of their ticket for whatever reason but who thinks they have a genuine claim to the prize notifies us in writing by 5pm on January at the latest.
“We’re doing all we can to reunite the ticket-holder with this amazing £40 million win – one of the biggest unclaimed prizes ever.
“The festive period is such a busy time for everyone and in all the excitement it’s possible that the winning ticket might have been somehow misplaced.
“What a start to the new year it would be for the lucky ticket-holder if they were to check their tickets and claim their prize.”
If no one comes forward before the final deadline, the prize money, plus all the interest it has generated, will go to help National Lottery-funded projects across the UK.
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