Susan and Ivan Westbury, from Nottingham, matched all six numbers in Saturday’s jackpot but found out only when they took the ticket to Tesco to check.
“I was in shock,” Mrs Westbury told a news conference.
“The young assistant took my ticket and said that I should phone the Post Office,” she added.
A manager then took Mrs Westbury aside and advised her to contact Camelot as she had won the top prize.
She asked the shop assistant to call her husband to tell him about the win but he refused to believe it was true.
“I said to him you’re winding me up,” Mr Westbury said.
“He assured me he wasn’t and I thought I had better get to Tesco.
“When I got there Sue was in tears and I decided to go back into Tesco and buy a News of the World to check the ticket against the numbers.”
Once the couple realised they had scooped millions they drove around in a daze unable to believe the win before Mr Westbury returned to work, running his own lightning protection business.
“I’ve got a passion about work, it’s more than a business to me. I just love what I do,” he said.
He admitted he had not taken a day off work in four years and still plans to keep running his business, although working only “three or four days a week”.
They are also planning a holiday in September, a newspaper readers’ offer costing only £9.50 each, and chosen so they could take their dog.
The couple have three children and seven grandchildren and plan to share their new fortune with family members, along with buying a house and a car.
Their winning numbers were 15, 28, 32, 43, 44 and 45.
Source: Press Association