Theo and Millie were born last Thursday (pic: MEN Syndication)

Beth Ryder, 35, of Mount Pleasant, Rawtenstall, Lancashire gave birth to 10lb 9oz (4.8kg) Theo and his 8lb 3oz (3.7kg) sister Millie last Thursday.

The student nurse, who has four other children, said she was shocked when she found out how big they were.

"The doctors and nurses said they were going to be big, but not this big," she said.

Father Steve Ryder, 32, a security guard at Manchester University, added: "I knew they might be a good size. They said at the hospital that they had never seen twins that size before."

Mrs Ryder said her son Callum weighed in at 12lb 1oz (5.5kg), while she herself weighed 11lb 13oz (5.4kg) and her sister Claire was born 12lb 2oz (5.5kg).

'Big relief'

Her twins Theo and Millie missed out on being Britain's heaviest twins by just 6oz (170g).

She said: "There is no secret to it, I think it's just all genetic. Before giving birth I was massive. I couldn't even sleep and it was very uncomfortable. It is a big relief now."

Carol Boothman, who works in the maternity ward at Burnley General Hospital, said: "In our memory it is the biggest set of twins delivered in the Edith Watson Unit.

"All the staff are delighted that everything went well."

Twins usually struggle to meet the average newborn weight of 7lb (3.2kg).