Tickets for this summer's World Cup have been illicitly advertised for almost 40 times face value on secondary seller websites.
Fans heading to Russia risk being denied entry to matches if they show up with passes bought through a third party, Fifa has warned, saying it retains exclusive selling rights. Fifa says it regards the "illicit sale of tickets as a very serious issue".
Tickets were on sale in March for as much as £5,618 each across five separate sites including StubHub and Ticombo, according to consumer group Which?
A pair of premium category one tickets for the England v Tunisia match on June 18 were found listed for between £480 and £11,237 despite being advertised for £296 on Fifa's website.
But, Ticombo said it was not violating any legislation by trading tickets.
StubHub said: "We do not allow the resale of World Cup tickets on Stubhub.co.uk.
"Unfortunately, World Cup tickets were, due to a technical error, viewable from (but not purchasable on) our UK site for a limited period but this was promptly fixed."