Passengers using the new Channel Tunnel rail terminal in north London could face a long walk with their luggage because of a funding delay.
Passengers face a 10-minute walk to the Channel Tunnel rail terminal
The Government has not decided whether to fund the £70m needed to complete a new Thameslink station link with the Eurostar terminal at St Pancras.
Without funding, trains will pass through the station without stopping.
Passengers will then travel to the existing Thameslink station, with a 10- minute walk to the Eurostar terminal.
Brian Cooke, chairman of the London Transport Users Committee, said: "Passengers travelling on Thameslink from Gatwick and Luton to St Pancras will be hugely inconvenienced."
LTUC is concerned that the existing Thameslink station could become dangerously overcrowded when Eurostar trains start using the redeveloped St Pancras in two years' time.
A Department of Transport spokeswoman said it made sense for the new link station, which is being built below the new Eurostar terminal, to be developed.
"Ministers have said they are committed to the new station but the funding and timing is now being considered," the spokeswoman added.
From 2007, Eurostar services to London will stop at St Pancras, instead of Waterloo, in order to free up domestic train routes into Waterloo.