Knife crime is a major problem in several parts of Scotland

Bail will be opposed when there are similar previous convictions, more cases will go to jury trial and there will be stiffer sentences.

Lord Advocate Colin Boyd QC unveiled the changes at a Violence Reduction Unit seminar at The Hub in Edinburgh.

Mr Boyd said more than half of all murders were committed with a knife.

He told BBC Radio's Good Morning Scotland programme: "All you have to do is to speak to some of the casualty surgeons in our hospitals and also speak to prosecutors who daily have to look at the mortuary photographs and speak to the parents of those who've died, to appreciate the scale of the problem.

We need to start somewhere and this is just a key element of that Det Ch Insp John Carnochan Strathclyde Police Send us your views

"If you carry a knife in a public place then you will be arrested, you will be taken into custody and you will appear in court from custody, you won't be bailed by the police."

He added: "We all know that in particular parts of Scotland, in our communities, knives are regularly being carried, by young men predominantly, who take them out almost as a matter of course.

"Just like dressing to go out, the added accessory is a knife."

The lord advocate said the new guidelines were likely to be widely enforced.

Mr Boyd said: "Of course they're discretionary, because there will always be exceptions to the rule, but I expect prosecutors will follow them very, very closely indeed, and that will be monitored."

KNIFE CRIME GUIDELINES Anyone caught with a knife will be arrested and held in custody Bail will be opposed where there are previous knife or violence convictions Cases will be referred to higher courts if there are similar previous convictions, meaning tougher sentencing Prosecutors will seek curfew and "exclusion zone" conditions An amnesty to allow the surrendering of knives

Det Ch Insp John Carnochan, from Strathclyde Police's Violence Reduction Unit, warned offenders they would be caught.

There were 1,301 knife attacks in Strathclyde last year, 1,100 in a public place involving non-domestic knives

Det Ch Insp Carnochan welcomed the new guidelines, but said a culture change was the only way to tackle knife crime

He said: "I don't think that anyone, from the lord advocate and the first minister down, thinks that this will solve the problem - it will not.

"But it's part of a whole range of other things that will happen now, will happen over the next 12 months, five years, 10 years, the length of time it will take to change, but we need to start somewhere and this is just a key element of that."

The new measures will be brought in following a knife amnesty which runs from 24 May to 30 June.

'Dither and delay'

The Scottish Executive plans to double the sentences for knife possession from two to four years and increase the minimum age for buying knives from 16 to 18, in measures being considered in the Police, Public Order and Criminal Justice (Scotland) Bill.

The Conservatives criticised the executive for not introducing the measures sooner.

Tory MSP Margaret Mitchell said: "This is yet another example of dither and delay from Labour and the Liberal Democrat, when decisive action was required."

She also claimed more needed to be done to educate pupils in primary and secondary schools about the consequences of carrying knives.