eurostar trains

[johnvincent1]

How many eurostar trains would be travelling on the railway lines at any one time?

[mushroom25]

at certain times of the day there is one train per hour London-Paris (journey 2h15mn), and one train every 2 hours London-Brussels (journey just over 2h). During one of those hours there will be 3 London-Paris services moving and one, possibly 2 (at least for a few minutes) London-Brussels services. So potentially there's up to 5 trains in each direction, but that probably wouldn't add up to 10 as the return trains aren't at the same times as London departures.