The lucky holder of the EuroMillions UK Millionaire Maker ticket with winning code TQQN 21656 from July has until Wednesday, January 15, to come forward.
Andy Carter, from The National Lottery, said: “Time really is running out for the winner of this prize, but we are still hopeful that someone will come forward at the very last minute to claim the money.
"We’re urging everyone to check their old tickets one final time or look anywhere a missing EuroMillions ticket could be hiding.
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"This life-changing prize could really help to make dreams become a reality for someone out there and what a start to the new year it would be for this lucky ticket-holder if they were to come forward in time.”
EuroMillions UK Millionaire Maker guarantees a £1m prize every time but in the special draw on July 19, 20 millionaires were made.
For every EuroMillions line played, UK players automatically receive a Millionaire Maker code printed on their ticket, with one £1m prize guaranteed in every draw.
But in the special draw on July 19, when the winning Northampton ticket was bought, 20 millionaires were made, with 180 days to claim the prize.
If no-one comes forward with the winning ticket before the deadline, then the prize money, plus all the interest it has generated, will go towards National Lottery-funded projects across the UK.
In the Northampton area, more than 1,000 National Lottery grants have been awarded.
Anyone who believes they have a winning ticket, for this or any other draw, call 0333 234 5050 or email [email protected]