RESIDENTS who persistently use their front gardens as driveways without getting the council to lower the pavement could find their paths blocked off.

Harrow and Brent councils have both defended the practice of putting up concrete bollards in gardens that have been "unlawfully" converted into drives, but said the measure would only be used as a last resort.

The policy is intended to stop drivers damaging the pavement and reduce the cost of repairs but in Brent at least one resident has seen them installed while his car was still parked in the drive.

Brent Council has installed bollards on 33 occassions since the beginning of 2007 at an average cost of £400 to 600 per site.

James Diamond, a spokesman for Brent Council, said residents are informed in writing before the bollards are put up and asked to remove their car from the drive. He could not confirm how many cars had been trapped.

He said: "Residents who have unlawfully constructed the crossings themselves are first informed in writing that they must apply to have a crossing constructed by this highways authority, or we may install posts to prevent their access.

"We have a zero tolerance policy on illegally constructed crossings.

"We will take action to ensure such practice is discouraged, including writing to the resident to make them aware of the consequences of not complying with legislation."

Harrow Council could not confirm outright that none of the bollards already installed have trapped cars in their drives.

But Paul Masterman, a spokesman for Harrow Council, said: "The council wouldn't do that. The point of this is that it is being done for the benefit of everyone in Harrow in terms of saving Council Tax money."

The authority offers residents the chance to pay for the pavement to be lowered before putting bollards in place, a conversion which can cost anywhere between £400 to £1,500.

The council does not have figures for how many have been installed.

Mr Masterman said: "This happens in a minority of cases, where people still carry on driving over the curb and creating damage to the pavement. We are not just doing this arbitrarily."