Police investigators have concluded there is insufficient evidence to substantiate a young British woman's claim in UK media that she was raped on Koh Tao in Surat Thani in June.

National police chief Chakthip Chaijinda said on Tuesday the young woman had been questioned recently by investigators and she was unable to give details of the rapist or the crime scene.

Forensic tests also found no traces of semen on her shirt, only traces of other DNA.

Police investigating the case claimed they had looked thoroughly into all aspects of it - starting with the interrogation of officers at the police station responsible for the area, inspecting the alleged crime scene, and sending investigators to question the woman in the United Kingdom and bring back evidence for examination.

Investigators were sent to the UK to verify claims by the 19-year-old she was drugged, raped and robbed on Sairee beach of Koh Tao on the night of June 25.

She said in stories published in British newspapers that she fled to the neighbouring island of Phangan, later returning to Koh Tao to file a complaint with police she accused of refusing to investigate her rape complaint and noting only details of the robbery.

Pol Lt Col Piyapong Boonkaew, chief inspector of  Koh Tao police said he was one of the investigators who questioned the woman in the UK.

They had asked her about the crime scene and showed her photos of the beach where the alleged rape occurred and nearby areas on Koh Tao.

She was unable to identify the alleged crime scene. Nor was she able to describe her attacker. 

She gave insufficient details to back up the rape story, Pol Lt Col Piyapong said.

Pol Maj Gen Pridi Pongsetthasant, deputy chief of the Office of Forensic Science, said an examination of the T-shirt the woman said she was wearing that day found DNA traces from a woman and a man. There were no traces of semen on the T-shirt as alleged.

Asked if legal action would be taken against the woman for filing a false complaint, Pol Maj Gen Surachate said no complaint had been filed at this time. Police have not so far blacklisted the woman and denied her further entry to Thailand.

Police earlier said they would blacklist the woman and deny her entry to Thailand if she failed to disprove investigators' findings that her rape claim on Koh Tao was groundless.