Virgin is talking to London & Continental, which will design and build the terminus and the 68-mile Channel Tunnel Rail Link which will cut London- Paris journey times to 2 hrs 20 mins.
L&C's Eurostar trains will operate from St Pancras, but surplus capacity will be available to other operators.
Virgin, which operates the West Coast main line franchise serving the Midlands, the North-west and Scotland, wants to supplement Eurostar's planned services such as Paris-Birmingham (4 hrs) and Paris-Manchester (5 hrs). A spokesman said: "It makes sense for us to pick up passengers from intermediate stations and drop them at St Pancras, where they will have a platform-to-platform connection."
The Order authorising the connection between the Channel link and the West Coast line will be discussed in parliament this week. Existing track, running 700m across railway lands at King's Cross, could allow trains from the continent to make their way directly north, saving 20 minutes on journey times for the nine Eurostar trains a day planned to serve the Midlands and the North.