The prime minister has rejected Tory claims that new powers for police to fine criminals are a "shoplifters' charter".

Tony Blair was forced to defend the policy after a Commons assault by Michael Howard.

The Conservative leader said a law that came into force on Monday would punish shoplifters as if they were guilty of parking on a double yellow line.

"Why does the prime minister think that shoplifters shouldn't get a criminal record?" he asked.

Responding, Blair insisted that the fixed penalty notices were an option but "the full criminal law still remains".

That failed to satisfy Howard, who said that "shoplifters will no longer get a criminal record".

"Shoplifters are being told that they can steal up to £200 of goods and in exchange get a fixed penalty notice of £80, right? Take £200 and get fined £80," he said.

"This week the government produced a charter for shoplifters. Is that what the prime minister meant when he talked about being tough on crime?"

But the prime minister told MPs that Howard's arguments were "getting worse".

Blair said that police officers had the discretion to decide whether to issue an on-the-spot fine or instead arrest and charge the suspect.

"Fixed penalty notices... have now been welcomed by the police right across the country," he said.

"They are not a substitution for the existing criminal law, they are in addition to it."