A £41 million EuroMillions jackpot remains unclaimed after the draw earlier this month.
The search for the mystery winner begins in Dorset, as National Lottery operator Camelot has revealed the south west county as the location of sale.
The numbers drawn a fortnight ago were 18, 31, 32, 38 and 48, with the Lucky Star numbers 04 and 12.
The holder of the winning ticket has until May 3 to come forward.
Camelot are urging players to check whether their ticket is the one matching all seven numbers.
Senior Winnings Adviser Andy Carter declined to reveal any further details in case the winner wishes to remain anonymous.
However, residents all over Dorset may well be rubbing their hands following Tuesday's announcement.
"What we know about people that win these large amounts of money is they have a chance not just to change their lives but those around them, and change the lives of people in their family for generations to come," Mr Carter said of the jackpot.
This is the third month in a row that there has been a UK winner, after West Sussex builder Steve Thomson won £105 million last month.
Following his win Mr Thomson said “it’s going to be a good Christmas” but pledged he would not give up his job.
He did say he would be “sensibly generous” with his windfall, adding: "I live in a small village, I do not want to leave the village, whatever I can do for the village, I will."
Andy Carter, Senior Winner's Adviser at The National Lottery, said: "£41 million is a huge amount of money coming up to Christmas - it's a huge amount of money any time of the year".
The mystery winner is also the seventh Brit to buy a winning ticket this year.
Another winning ticket was announced in the National Lottery's Rolldown draw last night.
A staggering 5,500 millionaires have been made since the lottery launched in 1994, according to the statistics, and 168 of them live in the UK's second biggest city.
There hasn't been a EuroMillions winner from Dorset, though 2015 Trevor Boyce winner speculated he and his wife would spend their £1 million jackpot on a move to the Jurassic Coast.
Viv Moss, a South Western winner back in 1998, described the announcement as being "like an unexpected death."
She went onto suffer from sickness and diarrhoea for a fortnight after her £6 million win.
If the winner is unlucky enough to have lost or damaged their ticket, they can still come forward.
They have another sixteen days to submit a written claim to Camelot, whose licence permits pay out up to 180 days after the draw.
Mr Carter and seven senior staff remain on standby to assist the winner should they come forward.
If no one comes forward the prize, and any interest generated, will be donated to National Lottery projects across the UK.