Police are looking for two men suspected of trying to steal laughing gas canisters from St Helier Hospital in Carshalton.

The pair were captured on CCTV walking around the hospital and then caught breaking into a lock-up containing nitrous oxide, police say.

When challenged, the men dropped a gas canister and ran off towards Tweeddale Road.

Police turned up and chased them on foot along Shaftsbury Road but then lost sight of them.

A drug canister worth £400 was damaged during the attempted theft on August 18 at about 12.45am.

Both suspects are described as slim white men in their early 20s.

One was wearing a white T-shirt, camouflage baseball cap, dark coloured trousers, white trainers and a gold chain. He was carrying a Nike bag.

The other was wearing a grey Duffer jumper, dark coloured trousers and dark trainers. His hair was shaved at the sides and he was also carrying a bag.

Detective Constable Paul Haridimou, from Sutton CID, said: “This was a callous and dangerous act. The suspects damaged the canisters unaware if they were in use by someone in greater need within the hospital.”

Anyone with information should call police on 101 or Crimestoppers anonymously on 0800 555 111.