An internal investigation has been launched by Brent Council after it installed wrong sized speed bumps on roads in Willesden.

Cllr Carol Shaw, who represents Brondesbury ward, demanded answers via the Freedom of Information Act over the blunder which resulted in residents being blighted by noise and vibrations from lorries outside their homes in Donnington Road, Peter Avenue and Chambers Lane.

The council refused to answer Cllr Shaw’s questions on who authorised the work, why the design errors were not picked up and what measures were taken to prevent a repeat fiasco.

The response stated: “None of the questions relate to data held by the council.

“They are not therefore subject to, or relevant to, freedom of information legislation.”

But the response revealed an internal investigation, led by an external investigator, is being held to look at system failures and, or, staff involved and their “adherence to quality assurance and other checking processes.”

The response continued: “Subject to the outcomes of this investigation, the head of service in consultation with human resources will consider whether and what action should be taken.”

The council also refused to say who was responsible for the design of the humps, saying that such a disclosure would be unfair and breach data protection.

The humps, which were too wide, have now been altered but the council has refused to tell the Times the cost to the taxpayer.

Last week, residents sounded concerns that a weight restriction on lorries using the roads was not being enforced.

A council spokesman said: “Residents have complained about the volumes of skip lorries and other HGVs travelling through the area, so the council have arranged for the enforcement of the 7.5 tonnes weight restriction in Donnington Road and the surrounding area using CCTV camera enforcement vehicles.

“The council will periodically visit the location to ensure that motorists are complying with local traffic regulations.”