A man who illegally built a major rooftop extension has been fined more than £40,000 and told he acted with the 'utmost stupidity'.

Mayur Naturbhai Patel extended his four bedroom terraced house at 104 Portland Road, in Holland Park, Kensington without planning permission and was fined £15,000 at Isleworth Crown Court yesterday.

He had £25,350 confiscated from him and was ordered to pay the Royal Borough of Kensington and Chelsea costs of £3,580, risking 15 months in prison if he fails to pay the confiscation order in three months.

The 1,741 sq ft five-storey house was bought for £1,650,000 in November 2011 and was put up for sale in March 2014 for £3,350,000.

Patel, currently of Academy Place, Isleworth, pleaded guilty to breaching the Town and Country Planning Act 1990 on June 10 after he added a large roof extension and a rear roof without planning permission in the exclusive neighbourhood.

Complaints from neighbours encouraged the council's enforcement officers to inspect the alterations which harmed the appearance of the Norland Conservation Area which Portland Road is part of.

They gave Patel four months to restore the property to ensure he did not profit financially from the extra floor space but despite a number of reminders most of the work still remains.

Patel, who has no previous convictions, claimed he received verbal confirmation from his architect and a planning officer who said the alterations would be acceptable.

Sentencing, Judge Phillip Matthews said he did not feel Patel broke the law because of shady motives but thought he had acted with the 'utmost stupidity' and it was no mitigation to say he relied on his architect's advice.

The council's planning boss, Tim Coleridge, added: “I am very pleased that the court has made this ruling. We were determined that Mr Patel should not gain financially from his illegal development.”