The winner, who was yesterday being interviewed by officials, was last night considering whether to go public.
The win will make him or her as rich as the rock star David Bowie and the actor Roger Moore, both estimated to be worth about £20m.
The size of the jackpot on Saturday was swollen by the £6.9m rolled over from the week before, when no one won the top prize. That had record sales of 61.5 million tickets - up 27 per cent from 48.2 million for the previous draw.
Unusually, the winning numbers were all above 25. They were: 26, 35, 38, 43, 47, and 49. The bonus number was 28.
Some newspapers had put teams of reporters on to the job of finding the winner yesterday. Most received calls from readers attempting to inform on friends or neighbours to claim the £5,000 reward offered for information on the winner by the Sun and DailyMirror.
The total prize pool was £34.5m. Of the £61.5 m spent on tickets, about £15m will go to causes, including charities, arts, sport and heritage.
The payout is by far the largest to go to one individual in the lottery's four-week history, although it does not compare with the $100m jackpots in the US.
The lottery's winning numbers will appear in the Independent every Monday from next week.