Jonathan Giles was found guilty of arson

Jonathan Giles had previously been found guilty of setting fire to Penyrheol school in Gorseinon in March.

The blaze, which is thought to have started in a bag of paper meant for recycling, destroyed 40 classrooms.

Giles, from the Loughor area, who was 17 at the time of the offence, was sentenced at Swansea Crown Court.

He had admitted burglary at the school but denied arson, blaming it on his co-defendant James Green, who was cleared of the charge by a jury in October.

The whole family feel terrible about what's happened Jonathan Giles' mother, Leiza

The fire, which was started early on 18 March, was so ferocious that it was too dangerous for fire crews to enter the school.

It continued for several hours, causing extensive damage.

Only two classrooms and an annex remained and many pupils lost course work in the blaze.

Giles' mother, Leiza Giles, expressed her remorse for her son's actions outside the court.

She said: "The devastation was awful. The whole family feel terrible about what's happened."

The damage caused by the fire is currently estimated at £8m, but Swansea Council believes the final repair bill is likely to be double that.