A couple have been fined £14,000 and told to demolish a two-storey extension to their home after it was built without planning permission.

Ann Clark and her husband constructed the “incongruous and overbearing” structure at the back of their house in Park Road, High Barnet, in 2010.

A year later, council inspectors discovered the extension had been built without permission and issued an enforcement notice ordering its demolition.

The couple failed in an appeal against the notice but continued to rent out rooms in the extension after the court case in October 2011.

Barnet Council took the Clarks to court over the breach and on Friday Mrs Clark pleaded guilty at Willesden Magistrates’ Court to failing to comply with the enforcement notice.

She was fined £14,000 and ordered to pay the council’s costs, as well as being told the extension must be demolished.

In her defence, Mrs Clark claimed she had been badly advised by her architects, who failed to tell her planning permission was required.

She also claimed the couple would make a significant loss from the demolition of the building.

But the court concluded there was a “complete disregard” for the planning notice at a time when Mrs Clark continued to rent out the contained flats.

Councillor Joanna Tambourides, cabinet member for planning, said: “This was a high fine for a planning enforcement case, which reflects its seriousness.

“Mr and Mrs Clark have paid a heavy price for failing to abide by the rules, but planning regulations are there for a reason.

“I hope this serves as a warning to anyone undertaking building work that they need to check first if planning permission is required.”