As many of half of the probiotic drinks available could be ineffective, experts have said.

Speaking at a briefing in London yesterday, experts said that some probiotic drinks might not contain the number of bacteria advertised.

Professor Glen Gibson, an expert in food microbiology from the University of Reading, said: “As a rule of thumb you can trust the big manufacturers. On the other hand there are a lot of other products out there that no one's ever heard of, and this is where the problems arise.”