Camden Council, in north London, is to report the agencies after its trading standards officers visited seven local agencies to compare the prices they were charging for the musical Miss Saigon which is on at the Theatre Royal, Drury Lane.
On a Saturday night the cheapest seats - pounds 7.75 from the theatre box office - cost pounds 35.10 from the Seven Dials booking agency in Shaftsbury Avenue, 353 per cent more.
The survey showed that while that mark-up was the worst, it was common for some to charge three times the cover price, while others charged a quarter more.
Trading standards officers also noted that none of the agencies volunteered the face value of the tickets, as the code of practice on prices under the 1987 Consumer Protection Act suggests they should. When asked, only one gave the correct prices, one made a guess, and the remaining five did not say what they were.