Police in Watford have issued a warning about using nitrous oxide after a rise in canisters littering the town.

The warning comes following the discovery of discarded canisters in areas including Alban Wood, Harebreaks Recreational Ground, and Garston Park.

Nitrous oxide - also known as ‘laughing gas’ - is a chemical gas being used increasingly as a cheap and recreational drug.

It is largely inhaled, usually with the aid of balloons. It leaves users feeling euphoric and relaxed, with some experiencing hallucinations.

Prolonged use of nitrous oxide causes significant loss of vitamin B12, causing brain and nerve damage.

It has been associated with anaemia, tinnitus, numbness in extremities and even death.

Sgt Steve Alison, from the Watford Safer Neighbourhood Team, said: “We regularly receive reports from concerned members of the public who have found collections of discarded canisters, often in parks or other green areas.

"Not only does this blight those areas but there are also serious health risks associated with using the gas incorrectly and its sale is often associated with crime.

"It is illegal to sell nitrous oxide to under-18s and gas offered for sale on the black market may even have been stolen from medical centres or businesses that have a legitimate use for it.”

In January police seized a large nitrous oxide canister found at an address in Rickmansworth Road.

The canister was suspected stolen and a teenage girl was served with a youth caution in relation to this.

To highlight the problem, Sgt Alison is inviting local school pupils to design posters highlighting the dangers of using nitrous oxide.

The winning poster will be selected to be used in schools and public spaces around the town.

Competition entries should be marked for the attention of Sgt Steve Alison and delivered to Watford Police Station, Shady Lane, Watford, WD17 1DD, by May 14.