Football fans have been warned they could be left disappointed and out of pocket if they buy tickets for this month's Euro 2016 through unofficial websites.
Consumer group Which? has said a number of unauthorised online outlets have sprung up in the run-up to the international tournament, some charging up to £5,000 for match entry.
Second-hand Euro 2016 sales are only allowed through Uefa's resale site and - since admission to the grounds requires photo ID - supporters without official tickets could find themselves turned away at the turnstiles.
Prices are only expected to rise as the much-anticipated footballing showcase, due to start in France on June 10, gets closer, Which? said.
As well as breaching Uefa's policy on resales, several sites were also found to be in contravention of the Consumer Rights Act 2015 by not disclosing seat locations and hiding the ticket's original value, according to the group.
Which? director of policy and campaigns Alex Neill said: "If you haven't bought your ticket directly from an official source there is no guarantee that you'll be able to get into the game and you could be left thousands of pounds out of pocket.
"More must be done both in the UK and across borders to stop these sites breaking the rules and scamming members of the public."
Warning signs of fake sites for those hoping to get their hands on a coveted match ticket include places selling tickets in large volumes, recently set up websites and payment being required to be sent by wire transfer.
The call for vigilance was supported by MP Sharon Hodgson, who is co-chair of the all-party parliamentary group on ticket abuse.
She said: "The work Which? has been doing in recent months to raise awareness among consumers about the fraudulent activities of ticket touts and secondary ticketing sites is vital to ensure that fans are put first in this market.
"Which?'s warning to consumers ahead of Euro 2016 is an important one which will help raise consumer awareness so they don't get ripped off by scams."
Some of the sites contacted by Which? as part of its investigation included www.gettickets.com, www.atstickets.com and www.europeanchampionshiptickets.com.
It received no reply from any of the groups.