No one has yet come forward to claim their £63.8m share of the EuroMillions jackpot, a National Lottery spokeswoman said.
A UK ticket holder was one of two jackpot winners in Friday night's draw, the other being with a ticket bought in Belgium.
It was the sixth jackpot win in Britain this year, and the haul puts the lucky person on a par with other multimillion-pound jackpot winners including Colin and Chris Weir, from Largs in North Ayrshire, who claimed £161m last July.
Other big winners include an anonymous ticket holder who banked £113,019,926 in October 2010 and Dave Dawes and wife Angela, from Wisbech, Cambridgeshire, who claimed £101,203,600 last October.
The latest mega-pot came about because of a double-rollover.
Last Friday six people won £266,505.80 each after matching five main numbers and one lucky star, but no-one matched all seven to claim the £106m jackpot.
The spokeswoman said: "Lady Luck is clearly shining down on the UK once again with another big EuroMillions win this year - the sixth jackpot win this year.
"We're absolutely delighted that a UK ticket holder has scooped a £63.8m share of this massive jackpot, alongside one ticket holder in Belgium.
"We've got the champagne on ice and look forward to welcoming the ticket holder into the National Lottery millionaires' club."
The exact amount won by the lucky Brit was £63,837,543.60.