A potentially hazardous batch of heroin is circulating in Watford, police have warned, with four people having suffered medical episodes.

Officers have warned the public of the problem this afternoon (December 22), with the known incidents all being linked to the class A drug.

It also warned people to be “extra cautious” about the source of drugs along with several other pieces of advice for users.

They urged people to make sure someone trustworthy is present if using, never mix drugs, and look after friends while aware of signs of an overdose – for example loss of consciousness, shallow breathing, or blue lips or fingertips.

Officers also said Naloxone – which blocks opiate receptors in the nervous system – will not work on non-opiate drugs, but it is still always worth having kits available in any overdose situation.

A Herts Police spokesperson said: “We are currently making enquiries in relation to the origin of the affected batch of drugs.

“If you have any information which may assist our enquiries, please contact the non-emergency number 101 or report information online.”