Eurostar has revealed plans to run double-decker trains through the Channel Tunnel for the first time.
The cross-channel rail operator has confirmed it will order up to 50 trains from manufacturer Alstom, eventually increasing the size of its fleet by nearly a third.
The expansion plans would include investing heavily in a crucial London depot, it said.
But questions remain over whether the facility has enough space for both Eurostar and potential rival operators to use it.
Eurostar also said it would invest €80m developing the Temple Mills depot in London, which is the only depot in the UK able to accomodate the larger trains used in continental Europe.
That depot, owned by the government's London St Pancras Highspeed organisation, is currently exclusively used by Eurostar.
Eurostar is also the only company currently offering cross-Channel rail services between London and Paris, but others want to set up rival services.
Those companies include Spanish start-up Evolyn, Sir Richard Branson's Virgin and a partnership between Gemini Trains and Uber.
The Office of Rail and Road is reviewing proposals from these firms to use Temple Mills, as well as Eurostar's plans to increase services.
The regulator is expected to make a decision on access to the depot within weeks.