Ticket reselling sites are to be investigated and could be fined by the competition watchdog.

The Competition and Markets Authority said on Monday it would probe the whole market after it was revealed that touts bulk buy tickets for resale on the sites, pushing up prices. MPs warned in November of “disturbing” evidence of close relationships between touts and resale websites.

An earlier review of four large secondary ticketing sites – Get Me In, Seatwave, StubHub and Viagogo – found that “people are not getting the full range of information required by law when buying tickets put up for resale”, the CMA said.

Gig-goers are not always warned that they may be refused entry if they buy tickets from such sites and relationships between sellers and event organisers are often not made clear.

The CMA said that one website was not fully complying with their undertaking to properly inform customers and it is actively pursuing it to ensure obligations are met “in full”.

Andrea Coscelli, CMA acting chief executive, said: “A night out at a concert or a trip to a big match is something that millions of people look forward to. So it’s important they know who they are buying from and whether there are any restrictions that could stop them using the ticket.

“We have heard concerns about a lack of transparency over who is buying up tickets from the primary market. We also think that it is essential that those consumers who buy tickets from the secondary market are made aware if there is a risk that they will be turned away at the door.”

Vickie Sheriff, campaigns director at Which?, said tickets “shouldn’t be fed straight into secondary sites at consumers expense”, adding: “We expect the CMA to take strong action against ticketing sites and businesses not playing by the rules.’

In November, MPs called for an inquiry into ticketing sites amid claims of fraudulent activity by some touts. The Department for Culture, Media and Sport select committee accused the sites of acting like “old-fashioned fences”.

A spokesman for FanFair Alliance, said: “The dysfunctional market and bad practices of the big four secondary ticketing websites were laid bare before members of the culture, media and sport committee. We anticipate that a fuller investigation of this market will lead to much-needed reform.