Politicians, police and campaigners against gun crime have united to demand tougher punishments for gangsters carrying firearms.

They urged the Home Secretary to change the law so that carrying a firearm means a five-year mandatory sentence even for teenagers.

The problem of gang culture and gun crime was graphically exposed in Birmingham with the murders of 17-year-old Letisha Shakespeare and Charlene Ellis, aged 18, in Aston four years ago.

Yesterday, MP Khalid Mahmood warned the city still had a gun crime problem, and those involved were getting younger.

He was speaking as senior officers in the Metropolitan Police met John Reid, the Home Secretary, following a series of horrific murders in London.

Sir Ian Blair, head of the Metropolitan Police, has led the call for tougher sentences after three teenagers in the capital were gunned down in less than a fortnight.

Wednesday’s shooting of Billy Cox in his own home followed the deaths of James Andre Smartt-Ford and Michael Dosunmu, both also gunned down in the past two weeks.

The Criminal Justice Act 2003 introduced a mandatory five year sentence for illegal possession of a firearm, but only if the offender is 21. Sir Ian wants the age at which the sentence can be imposed to be lowered to 17.

Mr Mahmood said: "My concern is that when gang members have been locked up you find younger people stepping into their shoes.

"That is why we need to make sure the law is just as tough for people aged 17 who are carrying a firearm."

Refering to the 2003 Birmingham shootings, he continued: "These killings happened in my constituency, and there have been others. But police have had a lot of success by working with the community, including with some people who were involved in gangs in the past."

Home Office figures show that firearms offences fell by seven per cent in the 12 months to September 2006 in the West Midlands.

MP Steve McCabe (Lab Hall Green), who has campaigned for many years for tougher gun control laws, added: "I don't personally hold with this arbitrary distinction which says a person is culpable at 21 but not at 17."

Gleen Reid, whose son was murdered seven years ago, said people carrying firearms should be jailed for ten years rather than five.

She founded Mothers Against Guns after her 28-year-old son Corey was shot dead outside a Handsworth community centre.

"People think nothing will happen to them if they carry a gun if they are below 21," she said. "And even if they are 21 they don't take it seriously, because five years is not long enough.

"If they knew it was ten years, I'm sure a lot would think twice about carrying a gun."

Paul Snape, Deputy Chairman of West Midlands Police Federation, said: "If you are old enough to do the crime, you are old enough to do the time. I would like to see a mandatory sentence for anyone carrying a gun."

A Home Office spokeswoman said the Home Secretary was "not unsympathetic" to calls for tougher laws.

But Dr Reid observed parents also needed to take more responsibility for their children.

"These are terrible, awful, tragic crimes and no one must look for any excuses. We have to use a whole array of methods to tackle it, from police and prisons right through to demanding family responsibility."

Similar comments were made by David Cameron, the Conservative leader.

He said: "When you look at the people caught up in these events, what you see is a complete absence in many cases of fathers, and a complete presence of family breakdown."

Sir Ian called for changes to the law earlier this week when he said police had identified a "new trend" of teenagers and young teenagers increasingly being involved in killings and serious violent crime.

A huge number of factors were behind it, he said, only some of which were to do with policing. He said the lack of role models in some households was an issue.