The lucky person who scooped the £170million EuroMillions jackpot has yet to come forward, and may not even know they are now the country's biggest ever winner.
If nobody claims the prize a week after Tuesday's draw, National Lottery operator Camelot will announce whether the ticket was bought online or in a shop.
By now, the National Lottery would have emailed any winners who bought their tickets online to alert them of their prize - although there is no guarantee these have been opened and read.
The winner, who matched all five main numbers - 07, 10, 15, 44, 49 - and the two lucky stars, 03 and 12, has 180 days from the draw to claim the prize.
If the winner bought their ticket from a shop and has not come forward after around two weeks from the draw - in this case around October 21 - the National Lottery will reveal the area of the purchase.
The area will include around 100,000 people in order to balance the winner's right to anonymity with enough detail to encourage players to check their tickets.
A Camelot spokeswoman said it had taken some time for previous winners to come forward, including Lincolnshire builder Andrew Clark, who found the winning ticket for a £76m EuroMillions jackpot tucked in the visor of his van six weeks after the draw.
Mr Clark said he only checked his tickets around once every three months, and had even had some blow out of his van window.
Camelot said the £170m ticket-holder would have a dedicated winners' adviser to validate the ticket, pay out their prize and help guide the new winner as they "start their adventure with their life-changing win".
The winner will also have to decide whether to remain anonymous or allow Camelot to announce it publicly.
While Camelot said the decision always remained with the winner, it suggested that many found going public helped the news to "sink in", and allowed them to enjoy their money without worrying how to explain where it came from.
A £123m winner in June has never revealed their identity and Camelot would not say whether it was an individual winner or a syndicate.
The previous biggest UK winners were Colin and Chris Weir, from Largs in North Ayrshire, Scotland, who won £161m in July 2011.
Andy Carter, senior winners' adviser at the National Lottery, said: "Players all across the country are urged to check their tickets as soon as possible.
"As always, the team are on hand to support and help guide the new winner as they start their adventure with their life-changing win."
