Tory MP Patrick Mercer has called on the Commons to back his bid for a new law protecting the public when defending their homes.

Speaking during the second reading of his Criminal Law (Householder Protection) Bill on Friday, Mercer said the legal position on attacking intruders suffers from "chaos and confusion".

Arguing for a new law to clarify that all forms of violence used by householders confronted with by an intruder should be acceptable, short of "gross disproportionality", he said the current test of "reasonable force" was too vague.

The Newark MP and frontbench spokesman on homeland security has worked closely with his party leadership in picking an issue that will cause maximum embarrassment for the government in the run-up to the general election.

But the prime minister has insisted the law is already "crystal clear" and has refused to support the new measure.

Earlier this week the Association of Chief Police Officers and Crown Prosecution Service united to release a leaflet explaining the law to the public and pointing out that only extreme cases of excessive force have prompted prosecution.

However Mercer told an unusually large number of MPs for a Friday sitting that: "If this is a good law and it's working, why do we need an A4 leaflet to clarify it?"

"Where does the definition of reasonable force lie?" he added. "Clearly it is vague.

"This law simply doesn't make sense... and a law in which the public has lost confidence must be changed."

Support

MPs voted by 130 votes to four in favour of the private member's bill, although in the absence of government space to debate it the measure is still like likely to run of time to pass through parliament before the general election.

Alternatively, Labour could still use its Commons majority to defeat the bill in committee or at third reading.

Home Office minister Paul Goggins said that the current law allows householders to "go to quite considerable lengths" to defend themselves.

He also insisted the government was making clear that the current legislation offered householders sufficient protection, and pointed to a new leaflet that offered advice on tackling burglars.

"The more that we advertise the message that is in that leaflet, the better I think things will be," Goggins said.

Goggins said the phrase "grossly disproportionate" would not provide a clearer test than "reasonable force". "It would still require a judgment to be made," he said.

Tory leader Michael Howard said, if elected, he would introduce the bill in government time.

"At the next election people will face a clear choice: a Conservative government that actually puts the rights of homeowners first, or Mr Blair - who after eight years in power and just weeks before a general election - is still only talking about it," he said.