UK Health Security Agency are urgently investigating the suspected illegal sale of fake botox after dozens of botulism cases were reported in North East England.

28 cases, most of which are in the Durham and Darlington areas, have all been reported by people who had recently undergone cosmetic procedures.

Reactions have included severe drooping of the upper eye lids, double vision, difficulty swallowing, slurred speech and lethargy, according to the UKHSA.

The UK Health Security Agency, in collaboration with Durham County Council and other partners, has convened an incident management team to trace the origin of the toxic injections. Investigators are trying to determine whether the adverse events were due to the potency of the toxin or the method of administration.

On one night in June, five of the people affected all ended up in the same A&E department in Durham, according to the BBC, which cited internal hospital communications in showing that the local stock of anti-toxin was nearly exhausted, forcing medics to request more from London as they “braced” for more patients.

The Medicines and Healthcare products Regulatory Agency (MHRA) is now understood to be investigating the spate of cases.

Dr Alison Cave, the agency’s chief safety officer, said: “Public safety is a top priority for the MHRA. Our Criminal Enforcement Unit works hard to identify those involved in the illegal trade in medicines and takes robust enforcement action where necessary. This can include criminal prosecution.

“Botulinum toxin (Botox) is a prescription-only medicine and should only be available in the UK under the supervision of a doctor or other qualified healthcare professional

“Buying Botox and other medicines from illegal suppliers significantly increases the risk of getting a product which is either falsified or not authorised for use in the UK.”

Dr Simon Howard of the UKHSA said that agency was still investigating the cause of the cases, and said the practitioners associated with most of the cases were no longer carrying out the procedures.

“However, that does not mean that we may not see more cases as symptoms can take up to four weeks to develop although we are now seeing the number of cases coming forward decreasing which is encouraging news,” said Dr Howard.

“We will continue to work with our partners to reduce the public health risk and would advise people to make sure they take precautions when seeking aesthetic procedures.

“Anyone who has recently undertaken an aesthetic procedure, and is experiencing any of the symptoms listed, should contact NHS 111.”

Botulinum toxin is widely used to reduce facial wrinkles and treat muscle conditions. While cosmetic practitioners do not need to be licensed, the drug does. Only seven brands are licensed in the UK, with Botox the most well known.

When used correctly the amounts are small and side effects are rare. But unregulated toxin, or larger quantities, can attack the nerves and cause botulism, a potentially life-threatening condition that causes paralysis.