A young thug set a teacher’s hair on fire on a train.

The teenager held out a cigarette lighter which set light to the victim as she passed him in a carriage.

Last night police issued the images of four teenage boys they want to speak to about the attack.

They said the woman could have been seriously injured and urged the public to come forward if they knew the youngsters pictured.

The dangerous stunt came less than a year after an unprovoked attack which turned a sleeping man into a human fireball on a train travelling through Worthing last year. Four people have been charged over that attack.

The victim of the latest assault, a 24-year-old teacher from Sweden who was with a group of students on a visit to the county, was targeted as she walked along a carriage on a train from Sussex to London.

She only realised what had happened when her students started screaming and pointing at her.

She managed to pat the fire out before her head was injured.

Police said she was left singed and extremely distressed after the attack.

Inspector Gary Ancell, from the British Transport Police (BTP), said the incident, which happened on Sunday July 19, was being publicised and the CCTV released because other lines of inquiry had failed to identify the youths.

He said: “The victim was incredibly lucky because within a few more seconds the majority of her hair could have been on fire, causing her serious harm.

"Assaults of this nature are extremely rare on the railway system but I am treating this incident very seriously and urge the youths pictured in the CCTV images or anyone who recognises them to come forward.”

He said the attack could have been a prank gone wrong but was being treated as a serious assault.

Insp Ancell said: “It is a stupid thing to do. We are treating it very, very seriously.”

The attack happened at about 6.30pm as the train passed through Bexhill on its way to Charing Cross.

Afterwards the train’s conductor found two youths hiding in a toilet.

He then threw four teenagers off the train at Hastings.

The youths are believed to have taken another train to Robertsbridge, near Battle, and police believe they probably live in that area.

The attack came seven months after a passenger on a train passing through Worthing suffered major burns when his beard was set on fire.

Luke Kennedy, then 21, from Arundel, was left fighting for his life when his hair and beard went up in flames.

Two men and two youths are due to stand trial over the attack at Chichester Crown Court in October.

Anyone with information about the Bexhill attack is asked to call the BTP on 0800 405040 quoting background log B5 of August 12 or Crimestoppers anonymously on 0800 555111.