Donna and David Stickley were the sole ticket-holders, matching all five main balls using their regular numbers – 1, 15, 21, 30, 35 and 44.
However, they didn’t discover their good fortune until the following week when Ms Stickley found the ticket at the bottom of her handbag when entering the following week’s draw.
She initially thought she had won £2m, only to discover their winnings were actually £21,044,592.
Mrs Stickley said: “There were too many decimal points. It did not quite compute.”
The couple – who have been together for nearly 20 years but only wed in March – plan to spend some of their winnings on a beach honeymoon, as well as looking after elderly relatives.
Describing themselves as “shellshocked”, both say they intend to keep their day jobs.
Mr Stickley is an aircraft re-fueller at Babcock International, and Mrs Stickley works as an office manager at an engineering firm.
Mr Stickley explained: “This sort of thing does not happen to us… We are normal people. We do not want dramatic change…
“Now that everybody knows, we can crack on. Life goes on. I will back to work on Tuesday.”