The mystery winner matched their five numbers in the EuroMillions HotPicks draw with the five main numbers from the EuroMillions draw on March 13.
The shop which sold the golden ticket has not been revealed but lotto chiefs said it was in West Lancashire.
The winning EuroMillions numbers on that date were 3, 11, 21, 27, 36 and the ticket-holder has until September 9 to make their claim.
However, lottery players are being urged to check their tickets via the National Lottery website or app rather than taking a trip to the shops because of coronavirus.
Camelot’s Andy Carter, senior winners’ advisor at the National Lottery said: “We’re eager to find the mystery ticket-holder and unite them with their winnings – this amazing prize could really make a huge difference to somebody’s life.
“We’re urging everyone who bought a EuroMillions HotPicks ticket in this area to check their old tickets again or look anywhere a missing ticket could be hiding.
“In the current situation, rather than taking a trip to the shop to check your tickets, we’re encouraging everyone to check their numbers online via the National Lottery website or via the National Lottery App. While we are all trying to do the right thing by staying indoors at the moment, it’s a good opportunity to dig out and check those old lottery tickets.
“Look for that £1n pound ticket in the pockets of clothing, in wallets, bags and down the back of the sofa – someone out there could literally be sitting on a fortune! We have our fingers crossed that the lucky winner comes forward to claim their win.”
Anyone not in possession of their ticket, for whatever reason, but who believes they have a genuine claim can still make a claim in writing to Camelot, but it must be within 30 days of the draw.
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 help National Lottery-funded projects across the UK.
With all National Lottery draws, players have 180 days from the day of the draw to claim their prize if they have the winning ticket.
Anyone who has any queries or who believes they have the winning ticket for any of the National Lottery draws within the 180-day deadline should call the National Lottery Line on 0333 234 5050 or email [email protected]