Gangs of violent men from Sri Lanka are "constantly tooled up" and "ready to go", according to police.

There have been a number of violent clashes involving groups of Tamil men in Croydon and other parts of south London in recent years.

They culminated in the murder of 28-year-old Prabaskaran Kannan in Tooting last year. He was chased by a group of four men from Croydon who stabbed and slashed their terrified victim 31 times outside a fried chicken takeaway shop.

The chief investigator in the case which became known as the "Chicken Cottage murder" said Croydon's Tamil gangs were causing concern among officers.

Detective Sergeant Mick Snowdon spoke out about the problems surrounding Tamil gangs after five men were convicted of Mr Kannan's murder at the Old Bailey.

The court was told Mr Kannan was heard shouting "It wasn't me, it wasn't me" shortly before he was brutally set upon and killed.

On Monday this week homeless Vabeesan Sivarajah, 22, Aziz Miah, 20, of Sumner Road, Croydon, Asif Kumbay, 20, of Grasmere Road, Purley, and Kirush Nathankumar, 18, of Purley Way, Croydon, were all convicted of murder by an Old Bailey jury. They all denied the charges.

The young men burst into tears after the sentence was announced. A jury of nine men and three women took three days to reach their verdict.

The four were also convicted of causing grievous bodily harm and actual bodily harm to two gang members who were with Mr Kannan that night.

Another defendant, Mayuran Srivinayagam of Greyhound Terrace, Streatham, was cleared of murder and manslaughter but found guilty of assault.

Earlier in the trial a sixth gang member, Mahitharn Ratnasingham, of Lesley Grove, Croydon, was cleared of murder and manslaughter. He admitted assault. The men are due to be sentenced on July 7.

After the men were convicted Det Sgt Snowdon told the Croydon Guardian: "They the gangs are very violent. They are constantly tooled up and ready to go. It is almost like the level of violence is ad hoc. Whatever happens for them happens, and it depends on what weapons they have around."

A businessman who runs a shop in Croydon said Sri Lankan Tamil gangs controlled most of the crime and had the town centre on "lockdown."

Police have always in the past denied there was a problem with the gangs in Croydon, but have now admitted there was a specialist officer dealing with Tamil gang activity in the borough.

A member of a gang who did not want to be named said: "These guys are tough man, they do not care who they hurt or who gets in their way. They ride around in flash cars tooled-up with knives, swords, bats and whatever else they can grab to do damage to a guy."

Detective Inspector Anthony McKeown, from the Met's Homicide and Serious Crime Command, said: "Those who carried out the attack were from a gang of Tamil and other Asian youths from Croydon, who came to Tooting with the express purpose of attacking people whom they saw as members of a rival Tamil gang."