A yacht club moved to make way for The O2 at the turn of the century says its contract is not being enforced and is claiming another group of sailors have taken their pier.
Thames Barrier Yacht Club treasurer Geoff Cooper claims the Mudlarks jetty was built for the 24-year-old club's use back in 2000 after they were relocated to make way for the Millennium Dome - now The O2.
But he claims the club have now discovered that a separate organisation, called Thames Barrier Yacht Club Ltd, was set up at the time to run the pier on behalf of the Greater London Authority - and he says they are taking up the moorings and putting the 60-member club's future at risk.
He said: "We went to the GLA about it but they're not recognising us as a club. Meanwhile, they're not maintaining it, they're not looking after it."
Mr Cooper went on: "They're adamant that they're not recognising us and they want to let these guys push us off. They're saying we've got no standing, which obviously we're not happy about.
"The GLA should say 'we've seen your contract, it's an ongoing contract, you've go the rights to be there'.
"I've even written to the mayor but he hasn't bothered to answer."
A spokeswoman for the GLA said: "Thames Barrier Yacht Club was originally located on a jetty that was demolished in 1999 during the redevelopment of the riverside for the Millennium year exhibition held on the Greenwich Peninsula. Thames Barrier Yacht Club members were advised to join Greenwich Yacht Club a very short distance away and to use their moorings.
"The club itself was not relocated onto the new Mudlarks jetty.
"Thames Barrier Yacht Club Ltd has managed Mudlarks jetty on behalf of the GLA since 2000.
"This is a hugely popular site with only 20 spaces, some of which are reserved for the original members of the Thames Barrier Yacht Club, but anyone is welcome to apply to moor their boat at the site."