Born either side of midnight on the evening of Sunday, August 31, the sisters straddle the cut-off point for the academic year.

Lexus was born naturally, just 45 minutes before Amber was delivered by caesarean section on September 1 at the Barratt Maternity Unit in Northampton.

But parents Sarah Conway and Ian Caldwell are already determined the week-old twins will be taught together.

"There's no way you can have one sitting at home while the other one starts school," said Sarah. "They're going to school together. It's a shame they can't be a bit more lenient."

Ian, 42 and a twin himself, said the family would either have the girls taught at home, or would move to Spain if they were unable to start primary together.

Separate birthdays is also causing problems for vaccination dates and appointments, with Lexus being technically a day older than her sister.

Sarah, 37, an administrator, said: "With jabs and things, we're going to have to go again the next day for Amber. How do you have a birthday on one day and do it all over again for the other one? And how do you choose which day to celebrate both?"

After the difficult birth, the family is looking forward to settling into a routine and has already discovered the girls' different personality traits.

Ian, who chose elder twin Lexus's name, said she was already more "girly" than Amber, who was very laid back.

"They lay next to each other and Lexus stared lovingly at her and Amber just wasn't bothered," said Sarah.

She added: "They're here eventually, but they couldn't have come any harder. I want to thank the midwives at the Barratt unit; they were brilliant."