A general view of the Shrublands area of Croydon in London, Britain where police say a “brutal” attack involving a gang of up to 30 assailants on a teenage asylum seeker took place.

British police said they had now charged 13 people on Tuesday over a brutal attack on a teenage asylum seeker in south London which detectives said he was lucky to survive.

The 17-year-old Kurdish Iranian boy, named by media as Reker Ahmed, was set upon by a group of up to 30 people shortly before midnight on Friday as he waited at a bus stop with two friends near a pub in Croydon.

Police said the suspects had asked the victim where he was from and once when they discovered he was an asylum seeker they chased him before launching the assault which left him with a fractured skull and blood clot on his brain.

Immigration has been a major political issue in Britain and was one of the factors that swayed voters to back leaving the European Union in last year’s referendum in order to have more control on the numbers coming to the country. The Brexit vote also led to a spike in hate crimes.

Five people, three aged 20 and two aged 24, appeared in court on Monday charged with violent disorder over the attack on Ahmed. Detectives said another eight, including two boys aged 15 and 17 and a 17-year-old girl, would appear on court accused of the same offence on Tuesday.

Two men and one of the teenage boys are additionally charged with racially aggravated grievous bodily harm.

Detective Superintendent Jane Corrigan said as many as 30 people were involved in the apparently motiveless attack and the teenager was lucky not have been killed.

In a tweet after the attack local lawmaker Gavin Barwell described those responsible as “scum” while London Mayor Sadiq Khan vowed the perpetrators would be brought to justice.