- Police arrested the 26-year-old suspect, who was thought to have gone into hiding on a mountain close to the beach where the shooting took place, around noon (local time) on New Year's Day, according to reports;
- The Bankok Post said the suspect denied firing the deadly shot but admitting being involved a fight with a group of men at Zoom Bar, where Mr Ashton was partying.
A man is expected to be charged with manslaughter following an arrest, police in Thailand said.
Police said British tourist Stephen Ashton was with a group of friends and 300 other tourists on New Year's Eve.
They were celebrating the countdown to 2013 at a pub and restaurant called the Zoom Bar when he was shot by a home-made gun at Haad Rin beach shortly after 4am.
The Bangkok Post reported that he was visiting the island with four or five friends and was staying at Pink Bungalow on Haad Rin.
Police in Thailand have arrested a man after a British tourist was shot dead at a New Year's Eve party when he was hit by a stray bullet as he danced with friends.
Stephen Ashton, 22, is said to have been at a beach bar on the paradise island of Koh Phangan. Police Colonel Kittakarn Kramomthong, chief of police at the island's station, said officers had arrested a 26-year-old Thai man and confiscated a gun.
Friends have been paying tribute to Stephen Ashton on his Facebook page and on Twitter after the British tourist was killed at a New Year's Eve party in Thailand.
One person wrote: "Cannot believe what I've just seen...in complete and utter shock...thoughts are with you and your family".
Others described him as an "absolute gent" and a "lovely boy".
Another wrote on Twitter:
This amateur footage shows the bar where the shooting that killed the British tourist Stephen Ashton is alleged to have taken place.
It appeared to be business-as-usual in the street outside the Zoom Bar close to Haad Rin beach on the Thai island of Koh Phangan.
The newspaper cites witnesses who said that an argument broke out between two groups of Thai youths at Zoom Bar on Haad Rin Beach.
A member of one of the groups reportedly fired a shot into the crowd as he ran out of the bar, hitting Mr Ashton in his torso.
Police have reportedly arrested a 26-year-old suspect and plan to question him at Noon on Wednesday.
The Thai island of Koh Phangan, where 22-year-old Stephen Ashton is believed to have been killed in crossfire between rival gangs, is a popular party destination for tourists.
It is famous for its monthly Full Moon parties on Haad Rin Beach which draw thousands of tourists, especially at this time of year.
The Foreign Office has confirmed the name of the British tourist who was killed in Thailand as 22-year-old Stephen Ashton from Redhill in Surrey.