St Pancras is an admirable terminal since its renovation, and Waterloo wasn't bad either. But where else might have been eligible for use as an international station for London? Assuming, for the sake of speculation, that the land had remained in rail ownership and not been developed, the only ones I can think of are Broad Street and Bricklayers Arms. Broad Street, including the former goods station alongside, might have allowed a two-level station with separate arrival and departure concourses, but it looks unlikely that the platforms could have been made long enough for Eurostar. And where would the depot have been?
Bricklayers Arms seems more suitable as a large rail-connected site no longer needed for its original purpose. It would have been further out of the centre than any other London terminus (shades of the South Eastern's cheek in advertising it as a west end terminus in the 1850s!) and poorly connected for onward travel. At the very least, an extension of the Bakerloo from Elephant would have been necessary, to give no-change connections to Waterloo, Marylebone and Paddington, and one-change access to Euston, Kings Cross and St Pancras. Liverpool Street and Victoria would have been more problematic to get to. Once again, the depot site would have been a difficulty.
Kensington Olympia probably wasn't big enough, and the West London line is busy enough with its own traffic, and not capable of much expansion. On the other hand, depot access would have been even better than it was for Waterloo.
Bricklayers Arms seems more suitable as a large rail-connected site no longer needed for its original purpose. It would have been further out of the centre than any other London terminus (shades of the South Eastern's cheek in advertising it as a west end terminus in the 1850s!) and poorly connected for onward travel. At the very least, an extension of the Bakerloo from Elephant would have been necessary, to give no-change connections to Waterloo, Marylebone and Paddington, and one-change access to Euston, Kings Cross and St Pancras. Liverpool Street and Victoria would have been more problematic to get to. Once again, the depot site would have been a difficulty.
Kensington Olympia probably wasn't big enough, and the West London line is busy enough with its own traffic, and not capable of much expansion. On the other hand, depot access would have been even better than it was for Waterloo.