More than 1,000 people in Hertfordshire could face five years in jail if the Home Office does not adequately publicise a change in gun ownership laws, warns the British Association for Shooting and Conservation (BASC).

From May 1, it will be illegal to possess a Brocock gun without a firearms certificate but BASC argues that not enough people know about the new leglislation.

Brocock guns are small self-contained gas cartridge-powered pistols and their ban was agreed in the Anti-Social Behaviour Act 2003 to help cut down on the misuse of air weapons and immitation firearms.

It is already against the law to buy, sell or pass on Brococks and the association estimates that 1,100 people in the county risk imprisonment because they will not know they have to buy a firearms certificate before the May deadline.

A spokesman for Hertfordshire Constabulary said that people "need to hand them in otherwise we cannot guarantee that we won't prosecute them".

The guns on their own are not a threat but they can be adapted to fire ammunition bullet, she said: "We don't want them getting into the wrong hands".

Mr Mike Eveleigh, senior firearms officer for BASC, said: "It takes eight to ten weeks to process an application, and there are now four weeks to the deadline. It must be extended by several months while the Home Office has a publicity blitz. If this is not done, the police and courts could be swamped."

With a couple of weeks to go, BASC claims they have received little more than a poster, a sticker and a leaflet to distribute to its 120,000 members.

Ms Sue Hawkins, secretary of Harpenden Air Weapons Club, said that the BASC's estimate was too high.

At the club, very, very few people would be affected and the two or three people who had Brococks had the necessary firearms certificate, Ms Hawkins said.

She said the club heard of the law change from shooting magazines. She was also concerned that people buying licences for their Brococks were not being financially compensated.

The police spokesman added that Brocock owners who obeyed the law had nothing to worry about: "As long as they can prove they have submitted an application form before May it's fine."