Gordon Brown has defended gun crime penalties after the sentences handed to some offenders were criticised by a top police officer.

The Prime Minister spoke out after Bernard Hogan-Howe, the Chief Constable of Merseyside, said judges were sending an “inconsistent” message to criminals.

Mr Hogan-Howe believes too few offenders are receiving the mandatory minimum five-year term for possession of a firearm.

In today’s Times, he said: “Locally, there is evidence of sentencing where the power has been available and not been used and that is simply wrong.

“I want very heavy sentences for possession of firearms which would deter people from arming others or carrying guns themselves.”

The mandatory term was introduced in 2004 amid public concern over gun crime.

According to the Ministry of Justice’s (MoJ) most recent figures, the average sentence handed down for the offence in 2005 was 47 months and only 40% of offenders were given the mandatory minimum sentence that year.

The Prime Minister said sentencing was only one element in the fight against gun gangs.

He said: “The important thing about gun crime is that we have the policing and support for the police to enable us to root out gun crime.

“We had set sentencing that is very high - five years for possession of a gun - for magistrates to use.

“It is tough sentencing to take action alongside more policing in hotspots, more metal detection, more undercover policing, more stop and search powers, and more surveillance.”

Mr Hogan-Howe, whose force is investigating the shooting of 11-year-old Rhys Jones last year, has held meetings with the local judiciary and members of the legal profession to discuss the effects of gun crime on the community.

Last October, Natasha Peniston was jailed for just three years for possession of a gun which accidentally killed her 12-year-old daughter, Kamilah.

But, the court had heard, Peniston had been pressured by others into keeping the weapon and Mr Justice Holland said such exceptional circumstances justified the lower term.

On BBC Radio Four’s Today programme, the Chief Constable accepted that there were occasions when the minimum term was not appropriate.

“But I’m afraid those are very rare occasions and the thing is, we can get through to criminals if we start to sentence in the right way,” he added.

“The value of a gun, in cash terms, is very low - it can be as low as £500.

“Compared to other items that are sold and bought by criminals, it’s a relatively low sum and if we can get it into their minds that not only is it a low sum of money but you are going to go to prison for 10 years or 15 years they will listen.

“We’ve got to get that message consistently and I’m afraid at the moment I just think it’s inconsistent.”

Merseyside Police Authority said today that it fully backed the Chief Constable’s comments.

Despite the introduction of the minimum five-year jail term, the number of firearms offences continues to rise.

Gun crime rose 4% from July to September last year compared with the same period in 2006.

Shadow Home Secretary David Davis said: “The Government have patently failed to get a grip on gun crime, with a four-fold increase in gun-related violence under Labour.

“The problem is, they are happy to pass tough laws in order to get a good headline only to simply not enforce them - allowing the situation to deteriorate at great risk to the public.”

A Home Office spokesman said: “We introduced the five year minimum sentence as part of the Government’s fight against gun crime to ensure that those possessing prohibited weapons received a substantial sentence. The average sentence before the legislation was introduced was only 18 months.

“The legislation includes provision for the courts to consider where exceptional circumstances might make a lesser sentence appropriate. We have set in place tough legislation but it is appropriate that sentencing is ultimately a matter for the courts.”

A spokesman for the Judicial Communications Office said the police can appeal to the Attorney General if a sentence is felt “unduly lenient”.

He added: “The number of cases referred for failure to impose a mandatory minimum sentence is small.”