Media playback is unsupported on your device Media caption Norman Smith sat down with Ed Miliband to talk about knife crime, the cost of living and "generation rent"

Labour leader Ed Miliband has said he is "sympathetic" to Conservative plans for tougher sentences for knife crime.

Tory Justice Minister Chris Grayling wants to automatically jail offenders convicted twice for possessing a knife.

Deputy PM Nick Clegg has attacked the plan as a "headline-grabbing" stunt that could make crime worse.

But Mr Miliband said he did not agree with Mr Clegg and it was important to send a "strong signal" that carrying knives was "not acceptable".

The Labour leader's intervention means the plan, which is already backed by Home Secretary Theresa May, could potentially become law without the backing of both coalition parties.

More than 25 backbench Conservative MPs have put forward an amendment to the Criminal Justice and Courts Bill currently making its way through Parliament.

Downing Street said Prime Minister David Cameron will give "very serious consideration" to whether the government will support the amendment.

'Strong message'

Mr Miliband told BBC News: "We definitely do want to use the legislation to strengthen the law and we are definitely sympathetic to the issue of mandatory sentences after a second offence, after conviction for a second offence.

Image copyright PA Image caption Justice Minister Chris Grayling's proposal is said to have the support of at least 25 Conservative MPs

"We need to make sure it's done in the right way, but that's where we stand, because I think the public want to know that we are going to send a strong message to people who carry knives repeatedly that it is not acceptable."

Mr Clegg claims mandatory sentences would increase the prison population and harm efforts to rehabilitate young offenders, some of whom may be turned into "hardened criminals" by a spell in prison.

He insisted he was not "soft" on crime and said prison was the right option for violent offenders - but judges should be allowed to use their expertise and judgement in deciding on individual cases.

"It is better to be smart on crime than sounding tough but doing something that could actually end up increasing crime," he said on his weekly LBC radio show.

'Surprised'

In an article for the Guardian, the Lib Dem leader said Chris Grayling's plan was a "headline-grabbing" solution following the murder of the Leeds schoolteacher Ann Maguire, who was stabbed to death in front of her pupils.

Metropolitan Police Commissioner Sir Bernard Hogan-Howe said he backed Mr Grayling's plan for tougher sentences because similar measures for gun offences had led to a drop in the number of young people being picked up with the weapons.

He told LBC: "For me, it's vital we send a clear message to our young people."

He added: "They do hear simple messages. They have heard it about guns, I think they need to hear it about knives."

But Mr Clegg said mandatory sentences could lead to innocent people being imprisoned or young girls coerced by gang members into carrying weapons being jailed when they were really the victims.

"The police, quite understandably, often say they want new powers on the statute book and often politicians and Parliament say, 'Hang on a minute, we don't just constantly put new offences on the statute book without considering the knock-on effect on the prison population, on rates of re-offending'," he said.

He said if Labour backed the proposal it would be "clear that they have learned nothing from their time in government, when they let the prison population spiral out of control".

Conservative mayor of London Boris Johnson said: "Nick Clegg is wrong. I do believe it's vital that we work to educate and rehabilitate those caught up in the culture of knife-carrying but equally it is imperative that the police and the courts are given every support to tackle the scourge of knife crime.

"That means backing this amendment, not ducking the issue. I'm surprised by the stance of the deputy prime minister - an issue as important as this needs unequivocal cross-party support."

UKIP leader Nigel Farage also backed the idea of tougher knife crime sentences, saying: "I think we get to a position where unless there are harsh penalties nothing is going to change, so I think the idea that two strikes and you suffer the penalty of being put away, we've got to try something."

Caroline Shearer set up a knife crime campaign group called Only Cowards Carry Weapons Awareness after her son, Jay Whiston, was fatally stabbed in September 2012.

Calling for "protection, not politics", she said the Lib Dems were "detached from what is actually happening on the ground", and said jail sentences should be imposed after just one knife-related offence.

"Once is enough to kill, you do not need to give them a second chance", she added.