Ticket resale websites and the touts who use them could be fined after the competition watchdog launched an investigation into how the best seats are harvested and then sold on at huge mark-ups before fans can buy them at face value.

The Competition and Market Authority said it was examining suspected breaches of consumer law after reviewing the four secondary ticket companies – Viagogo, StubHub, GetMeIn and Seatwave – that sell on previously purchased tickets.

It will examine several areas of concern in the secondary ticketing market, including whether touts use “connections” at resale websites to gain an advantage over fans, such as information that helps them decide which tickets to market aggressively.

The probe follows increasing scrutiny of the sector by MPs concerned about the inflated prices at which tickets are being sold. Earlier this month hundreds of tickets to see Adele next summer appeared on resale websites for up to £9,000, the latest in a string of in-demand events seized on by the UK’s most successful touts.

Andrea Coscelli, acting chief executive of the CMA, 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.”

“If we find breaches of consumer law, we will take enforcement action,” he added.

Rules introduced in 2015 require ticket resellers to provide details of the block, row and seat number, as well as the face value and information about any restrictions. Last year, the CMA secured pledges from the main websites that they would improve the information provided to buyers.

The CMA said one site failed to comply with the demand to provide such information. GetMeIn, Seatwave and StubHub said they were not the site in question. Switzerland-based Viagogo did not return a request for comment.

The watchdog has powers to force firms which breach the law to provide undertakings to improve their behaviour, while the courts can impose fines on those who do not.

The CMA’s investigation will also turn the spotlight on the touts, who are already facing the prospect of a tax investigation by HMRC. Those found to be concealing their identities or ticket details could face court-imposed fines.

A CMA presentation given recently to the Society of Ticket Agents and Retailers, seen by the Guardian, states that even the very act of bulk-buying tickets for resale is illegal. This is because anyone masquerading as a consumer for the purpose of business is in breach of the Consumer Protection from Unfair Trading Regulations 2008.

The CMA’s probe will also examine whether major touts, some of whom were named in an investigation by the Observer, are exploiting “connections” at ticket websites. A whistleblower from one resale site said touts are sometimes handed inside information to help them grab the best seats at must-have concerts.

Consumer body Which? urged the CMA to stake strong action. Vickie Sheriff, director of campaigns and communications at the consumer body, said: “On numerous occasions we have found tickets being sold unlawfully, so we welcome the competition authorities taking action to tackle this.”

Labour MP Sharon Hodgson, who chairs the All Party Parliamentary Group on Ticket Abuse, said it was “paramount that enforcement action is taken seriously and swiftly”. She also called on the government to tackle “bulk purchasing” by touts, amid calls to criminalise the use of ‘bots’, automated software sometimes used to buy large numbers of tickets.

Despite the CMA’s probe, some ticketing experts expressed disappointment. Music industry group FanFairAlliance said: “UK audiences will continue to be frustrated that measures to genuinely fix ticket resale are not being taken sooner – and while other countries take swift and decisive actions, British fans continue to be ripped off by touts operating under cover on the Big Four resale sites.

“We call on the government to respond to recommendations made in the Waterson review on secondary ticketing, and welcome the potential of a full inquiry by the select committee in the new year.”

A government-commissioned review by Prof Michael Waterson concluded this year that ticket resellers that do not comply with last year’s rule changes should be taken to court. The government has yet to respond to the review.

Security consultant Reg Walker, who recently testified to MPs about “ticket abuse”, cast doubt on the CMA’s assertion that most ticket sites are now complying with consumer protection laws.

“Given the information in the public domain about all four websites, I fail to see how any are fully complying with the Consumer Rights Act, let alone just one.”

Walker called on the CMA to demand firms hand over records of the touts who use them, to establish whether they are breaking the law.