A building housing a climbing wall owned by Winchester College was set alight on Wednesday.

Fire crews were called out at 3.15pm to deal with the small roof fire in Beaufort Road. It is the second time in two months the facility has been on fire: it was hit by a suspected arson attack in February.

Investigators are treating it as suspicious and one witness saw two teenagers walking away before she noticed flames. The building was empty and no-one was injured.

Station officer, David Presswell, said: "We don't know what caused the fire yet, but it was brought under control quickly. Because of the previous fire, there was not a lot left to burn."

Janet Budd, who lives opposite and dialled 999, said: "The fire brigade arrived remarkably quickly. I could see flames and there was lots of smoke. I could also hear small explosions inside. It was only later I remembered two teenage boys walking away."

After firefighters put out the flames, they cut away the charred roof timbers to prevent them flaring up again.

Jeremy Bracknell, assistant bursar, said: "It is believed the two teenagers set light to the roof by holding a lighter to the previously-burned part of the building. I have informed our insurers and we have checked the rest of the school."

The future of the building now hangs in the balance, as insurers decide whether it is so badly damaged that it will have to be demolished.