A HALLUCINATING woman burned down a rented Pontypool flat after she dowsed her mattress in petrol and set it alight believing it was filled with rats, a court heard.

Teresa O'Halloran, 35, of no fixed abode, was suffering an episode of paranoid schizophrenia on November 10 2013 at the flat she shared with her boyfriend on Clarence Street, opposite the Hanbury Pub.

The pub's landlady noticed people run out from the property on the morning of the fire, O'Halloran just wearing underwear; Gareth James, prosecuting, told Newport Crown Court.

Twenty minutes later, the defendant and her partner Martin Cook presented at the Royal Gwent Hospital with serious burns and were transferred to a specialist unit at Morriston Hospital.

When firefighters searched the property they found a petrol can and cigarette lighter along with the mattress, which was completely destroyed.

The defendant initially claimed she had been filling a lamp with petrol and spilled some, but later admitted arson.

David Webster, defending, said she was "clearly delusional" at this point and as her condition stabilised she gave a more rational account.

"The mattress was torn open because she believed there were rats or something living inside," he said. "She can now give a rational explanation of the hallucinations she was experiencing at the time. Doctors are of one view that but for her condition, she would not have committed this offence."

Insulation between floors protected the rest of the building including a shop underneath but the flat itself was totally destroyed, Mr James said.

Landlord Robert Grimes had a bill of £31,000 for repairs, of which he had to pay £6,200 from his own pocket.

The court heard O'Halloran's illness was aggravated by substance abuse and not taking her medication but it was not self inflicted.

Judge Daniel Williams said there were some shoplifting convictions on her file. But he added: "There's no indication from your past that you are a person with an interest in setting fires. There can be no doubt you would not have committed this offence if you weren't suffering from a disorder."

He made an order under Section 37 of the Mental Health Act requiring O'Halloran to have hospital treatment at Llanarth Court.