But the lucky person will have an agonising wait over the rest of the holiday before the jackpot windfall can be officially confirmed, said a spokeswoman for the organisers, Camelot.
"A ticket holder has come forward who we believe has the winning ticket," she said.
"But the first banking day is Wednesday and we will not be able to check the ticket and confirm the win until then."
Camelot could not say if the winner was an individual or a syndicate.
The six winning numbers were 2, 3, 27, 29, 39, 44 and the bonus ball was 6.
This weekend's jackpot was £7,789,557 and the total value of tickets sold was £55.2m - a record for a week when the prize was not rolled-over.
There were seven Match Five plus bonus winners, each winning £342,398; 365 Match Five winners each winning £4,104; 35,321 Match Four winners each winning £93 and 987,567 Match Three winners each with £10.
Camelot was today beginning an investigation into a nationwide computer failure which cut off ticket sales to thousands of people after gremlins struck twice yesterday.
Labour MP Mo Mowlam called for an inquiry after she claimed many of her constituents in Redcar, Cleveland, had been unable to buy tickets.
Computer problems first struck as a third of ticket sellers tried to log on to their terminals. Lottery spokesman Peter Rae said: "The problems began at 6am when 30 per cent had problems signing on their terminals. It was a computer fault and took a couple of hours to fix. By noon the vast majority were back on."
And there were more problems on Christmas Eve when around 2,000 lottery computers in all parts of the country were out of action for about 45 minutes. Camelot described the day's second failure as "just a glitch in the system".
Ms Mowlam said: "I am calling for an immediate inquiry over the running of the lottery today."
Last night's lottery windfall came after the Archbishop of Canterbury, Dr George Carey, called for the jackpot to be cut to a more manageable sum.
"While a National Lottery is no doubt a fact of life in this country for the foreseeable future, and I am no killjoy, perhaps we should at least scale down the more excessive prizes and tone down the hype," he said.