Nine European countries participate in the EuroMillions lottery
Nobody has yet claimed a share of the 100m-euro (£91m) EuroMillions jackpot won by two British tickets on Friday.
Operator Camelot said that by Saturday evening there had been "no valid claims" of the UK's largest ever lottery prizes of £45,570,835.50.
If one person, rather than a syndicate, owns either ticket it will also be the UK's biggest ever individual win.
In May, a ticket bought in Spain broke the European lottery's record by netting a 126m euros (£110m) jackpot.
"We have plenty of champagne on ice and are looking forward to welcoming the lucky ticketholders to the National Lottery millionaires' club," said a National Lottery spokeswoman.
Until now, the biggest ever single win was by former Royal Mail worker Angela Kelly, from East Kilbride, South Lanarkshire, who scooped £35.4m in August 2007.
She offered her congratulations to the latest millionaires "on taking my National Lottery title".
"My win has enabled me to bring a great deal of happiness to my friends and family, which has in turn made me very happy," she said.
"I wish the new winner the best of luck."
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Mark Gardiner, of Hastings, East Sussex, shared £22,590,829 with Paul Maddison in June 1995.
He said: "I'd say to the winner - enjoy yourself, do the one thing you have always wanted to do or buy, treat yourself with an impulse purchase and then take two steps back to let it all sink in."
The winning numbers on Friday were 19, 43, 45, 34, 11 and the Lucky Star numbers were 5 and 9.
Nine European countries participate in the EuroMillions lottery - the UK, the Irish Republic, France, Spain, Portugal, Austria, Switzerland, Belgium and Luxembourg.