Exploitative landlords are under the microscope after a plane used thermal imaging to route out beds in sheds across the borough.

Harrow Council used the technology to examine 75 suspect developments based on complaints from neighbours, however more than 300 are now under investigation by the authority's planning enforcement team following the fly over.

Susan Hall, Conservative leader of Harrow Council, said: “The pressures of migration in London, fuelled by recent waves of new arrivals from Eastern Europe, are creating new stresses on local authorities that we just haven’t had to contend with before.

"What was once thought even just 18 months ago to be a problem for the centre of big cities is now rippling out to the suburbs."

The council just set aside £100,000 to tackle rogue landlords, and have conducted a number of visits recently including finding a room with three mattresses where occupants were charged £55 a week each to live there.

Ms Hall added: “The beds in sheds phenomenon means there is a hidden community springing up in the back gardens of our cities – in our borough alone the thermal pictures we receive suggest there are four times as many as we first suspected.

"These are people who use council services – like bin collection – but for whom we receive no extra funding.

“In many cases the people in beds in sheds are at the bottom of a pyramid of exploitation. But we get complaints from their neighbours that we cannot ignore, and it is not fair on them that these houses should turn into cash cows for opportunist landlords.”

The plane, which flew over Harrow at a height of 1030 metres, took the images over the course of three hours starting at 9pm on January 11, and officers have been examining the images since.

Harrow's war on beds in sheds was even praised by Nick Clegg, the deputy Prime Minister, last year.

Councillor Will Stoodley, who chaired planning committee under the Independent Labour administration until September last year, consistently raised his concern over the problem and the national legislation that allows landlords to apply for lawful development certificates which, after four years, legitimise any indiscretions such as renting outbuildings without the proper permissions.

Labour’s Councillor Bill Phillips even called the legislation ‘insane’ last year, calling for change.

Mr Stoodley said: "What was frustrating for us in that time was that we came across two applications to legitimise these buildings which residents had already warned officers about years back, but nothing was done because they said they were short staffed.

"While the planning committee is limited in what they can do once things get to that stage, no one was talking about beds in sheds until we started blowing the trumpet and the Harrow Observer began reporting on it. Now we have the funding in place."