The Bill began as a one-off drama in 1983

The episode, broadcast on Wednesday, featured an MS patient being told about a fictional drug, Plavitron, which could alleviate MS symptoms.

"It was grossly irresponsible of The Bill to make up a drug," said MS Society spokesman Chris Bentley.

ITV said it believed it had "told the story responsibly and sensitively".

There are few effective treatments for MS and any mention of a new drug generates a lot of hope and excitement in people living with and affected by the condition Chris Bentley MS Society

"We researched both the condition and possible treatments - existing and proposed - before and during the writing process," an ITV spokeswoman said.

She added: "It was certainly not our intention to offend or mislead."

Fictional places, names and products were featured in storylines "often for legal reasons", she said.

Mr Bentley said the MS Society's helpline had received a number of calls from people wanting to know more about Plavitron only to be told it did not exist.

"There are few effective treatments for MS and any mention of a new drug generates a lot of hope and excitement in people living with and affected by the condition," said Mr Bentley.

"People with MS have a tough enough time as it is without being misled over treatments," he added.

About 85,000 people in the UK have MS, a degenerative disease of the central nervous system.