© AP Tickets for Beyonce's tour are being advertised at £1,729, more than 14 times face value
Music and theatre tickets are routinely being sold unlawfully on the UK's biggest secondary ticketing websites, according to consumer magazine Which?
Under the Consumer Rights Act 2015, buyers must be told the original face value of any tickets being resold and, where appropriate, the seat numbers.
After investigating more than 200 listings Which? found "numerous examples" of the rules being breached.
The findings of a government report into the market are due on Thursday.
Are touts making pop concerts the preserve of the rich?
One Direction, Arctic Monkeys, Adele, Elton John, Little Mix, Mumford and Sons and Radiohead are among the artists who have called for action against secondary sites, which they claim prevent fans from buying tickets at face value.
Calls have been made to make touting a criminal offence for concerts, plays and musicals - as is already the case for sporting events.
Others want the government to prevent tickets being resold at a profit, capping the price at the original face value, plus 10%.
At the time of writing, some sites are advertising tickets to see Radiohead's shows at the Roundhouse, London, this week for £5,900 - 91 times the original face value.
Which? looked at listings for Beyonce's Formation Tour, Catherine Tate's comedy show, Jersey Boys, Magic of the Musicals and Wicked the Musical across the four main ticketing sites - Viagogo, Seatwave, Stubhub and Getmein!
Researchers posed as sellers to find out what information was required when listing tickets - but discovered that the information often wasn't displayed to fans.
It found that Viagogo failed to consistently list the face value of tickets for Beyonce and Catherine Tate, despite sellers being legally obliged to enter this value.
Instead, Viagogo's small print said the face value of each ticket was within a certain range. For Beyonce, this range was often very large - from around £40 to more than £200.
None of the Viagogo listings, and only one on Getmein!, showed seat numbers, and many of the listings on Stubhub and Seatwave gave only row numbers or section numbers.
Alex Neill, director of policy and campaigns at Which? said: "It is clear the protections put in place by the Consumer Rights Act aren't being followed by some of the biggest players in the market, and no action is being taken against them.
"The government must crack down on bad practice so that people know what they're buying and don't get ripped off."
In response to the report, StubHub said its sellers must comply with the law, but added: "There are instances where sellers may not have access to this information at the time of listing, as some primary vendors do not provide this at the time of purchase."
Seatwave, GetMeIn! and Viagogo declined to respond.
© BBC BBC
BBC Music homepage
Read all music stories