Thirty centimetres has cost a Surbiton couple the extension they need to enjoy their home into their twilight years and could even mean they have no external walls.

Tearful Farzad Shamsavari, 66, said a mistake by the builders meant plans were not stuck to, and last week they were served an enforcement notice by Kingston Council to get it knocked down or trimmed back.

Mrs Shamsavari and husband Ali, 64, remortgaged their home in Moresby Avenue, Surbiton, for £50,000 to pay for the extension and said they could not afford to put it right.

With advancing arthritis, the three extra rooms built downstairs were supposed to become their bedrooms in coming years.

Mrs Shamsavari, a clinical psychologist at Tolworth Hospital, insisted it was an innocent mistake.

She said: "It is very harsh and unrealistic. It will practically destroy us.

“If they demolish the extension we will lose our external walls and the house will become uninhabitable."

Neighbours complained about the extension when it was built in March this year and the family submitted a retrospective planning application, which was turned down in June for being too "bulky and overbearing".

The extension was built 3.3m deep, instead of 3m deep, a corridor extended 1.2m too wide and there was no permission for a raised decking area.

Councillor Frances Moseley stood by the council's unanimous decision.