Drugs giant GlaxoSmithKline have been ordered to suspend trials of an MS and Crohn's disease drug over its links to another withdrawn treatment.
The drug was supposed to finish trials in 2005
Between 10 and 20 British patients were involved in global trials of the drug known as SB 683-699.
It is in the same class of drugs as the MS medication Tysabri, withdrawn after two patients developed brain infections last month.
The halt was ordered by the US Food and Drug Administration.
A GlaxoSmithKline spokesman said the trials for the UK were only at the early phase one stage, where the drug goes into the human body for the first time.
In other parts of the world the drug had entered phase two, where the dose is refined.
Results of the drug were supposed to have been reported in the final quarter of 2005.
The spokesman said the drug "belongs to a different class of agents and therefore is unrelated to Tysabri.
He said the company was disappointed with the news.
GlaxoSmithKline had been developing the drug with the help of Japanese firm Tanabe Seiyaku.
Christine Jones, chief executive of the Multiple Sclerosis Trust, said: "We are pleased to see that prompt action has been taken to protect the interests and safety of patients, although we are unclear as to the precise relationship between Tysabri and SB 683-699.
"In the UK, investigations were at an early stage and so considerable further research would have been required before any firm conclusions could be made about the role of this compound in the management of MS."