Fed up with not being able to enjoy leisure activities with their grandchildren, Roy and Kate Glencross decided to fight the flab and have the operation.

Both are now retired and want to spend as much time as they can with their family, but at the moment they have to sit and watch while their grandchildren play in the park.

Retired firefighter Roy, who weighs 24 stones, said they were both looking forward to the operation, which is due to take place at Peterborough District Hospital on June 10.

He said: "I have been on a diet for 15 years, I've tried them all, Atkins, Cambridge, but none of them worked.

"Weight would come off, but as soon as I stopped, it would pile back on.

"So three years ago I went to see a specialist at Peterborough hospital and he recommended either a gastric band or a gastric bypass.

"He said that if we carry on the way we are, we would have heart attacks before too long. We needed to change.

"Both Kate and I decided to do it together. We went for the gastric bypass. Once it's done, there is no way you can go back."

After marrying in 1983, Roy (60) and Kate (59), of Holbeach, near Spalding, used to enjoy a diet of biscuits, cakes, fried breakfasts and steaks. Now they have to change their diet completely so their bodies can adapt to the medical procedure.

Roy said: "The first week after the surgery we are only allowed a thimble full of water every half an hour. The intake gradually increases as our stomachs adapt. After two months, we will be having soups then soft foods."

The couple moved to Holbeach from London nine years ago. They have seven grandchildren, with another due in the autumn.

Kate said: "I want to be active. I want to play with my grandchildren and walk on the beach, but I can't at the moment."

Ideally Roy wants to shed six or seven stone – and he heard of people losing a stone a month after the operation. Kate wants to lose four.

Roy said: "Everybody seems to be surprised by what we are doing. We've agreed from day one that we would do it together.

"There would be nothing worse than if I had had the operation and then sat down to see my wife eating a lovely steak. It makes sense to do it at the same time."