The Times newspaper reported that more than 80 hotel and B&B owners have complained of being subjected to blackmail by customers.

Incidents included a demand for a 50 per cent discount on the hotel bill in return for not posting a one-star review, and false reports of food poisoning and theft being posted after guests’ threats were ignored.

On TripAdvisor’s own message board, a post from a disgruntled hotelier reads: “I am fed up of blackmail by guests either asking for upgrades and promising to put a good report on trip advisor (sic) or people who complain stating if we don’t get our money back + compensation I will put a bad review on.”

Industry insiders said that a bad review on TripAdvisor can cost businesses tens of thousands of pounds in lost bookings, as travellers tend to trust reviews posted by peers.

A spokeswoman for TripAdvisor reportedly said that threats are “strictly against our guidelines, but it may also be illegal”.

She added: “We take allegations of blackmail or threatening behaviour by guests against property owners very seriously.”

Launched in 2000, TripAdvisor attracts around 45 million unique visitors a month.