A planning loophole that had allowed UK car dealer sites to become general retail outlets without the need for planning permission is to be closed next month, according to the Retail Motor Industry Federation (RMI).

The new rules are being imposed by the government to curb the uncontrolled spread of out-of-town 'superstores' and the changes are included in The Town and Country Planning (General Permitted Development) (Amendment) (England) Order 2005, which takes effect on 21 April.

RMI legal director Graham Coleshill said: "Under the existing rules, certain kinds of car dealer premises could be converted for use as a shop without the need for planning permission, provided the change did not include physical alterations that would fall under general planning requirements.

"This enabled businesses operating large out-of-town showrooms to sell their sites to conventional retailers for use as superstores without the need for planning permission, and this is what government is trying to control."

The impact on most motor retailers will be minimal: "For most businesses the new rules will have little effect. The majority of small and medium-sized dealers are based in-town, and a change of use for them would entail building works, requiring planning permission.

"The rules are not intended to prevent dealers from selling their sites for conversion to superstores. The idea is to protect local business infrastructures from the effects of unplanned retail developments."