Theatre and music fans are to get better protection from hidden booking fees, after the Advertising Standards Authority ruled ticket retailers can't display prices without including compulsory booking fees.

The ASA is clamping down on sellers who display ticket prices online, but only reveal additional booking fees at the end of the transaction.

The watchdog upheld complaints about London venues The Old Vic and the Charing Cross Theatre, the Ambassador Theatre Group and arts marketing agency AKA Group for doing just this.

Three of the offending retailers have already amended their ticketing policies, while the Charing Cross Theatre says it is in the process of doing so.

The ASA says it will make sure today's ruling is followed by all ticket retailers, but its focus is clamping down on those selling tickets to plays, musicals, gigs, shows and concerts.

If retailers don't comply with the ASA's ruling, it can refer companies to the Office of Fair Trading, which can fine offenders.

ASA chief executive Guy Parker says: "These pricing practices are simply not fair. They draw us in on a false promise. They make us less likely to shop around for the best deal. Our rulings send a clear signal to advertisers: sort out your pricing so we all get a fair deal."