One-way fares on Eurostar...

There has always been a problem with one-way fares on Eurostar.  If you visit www.eurostar.com and ask for a one-way ticket from London to Paris or Brussels, they will often only offer you an expensive fully-flexible one-way business fare for £155, even on trains where there's a cheap return ticket available for as little as £59.  That's because Eurostar is trying to safeguard its business travel revenue.  So there are several different ways to get a sensible one-way price for Eurostar:

Experienced travellers use these methods to make affordable one-way Eurostar trips all the time, there are no problems with either of these options.  Unofficially at least, Eurostar realises it's getting your business instead of you switching to coach or air or train+ferry to find an affordable one-way fare..!