The Eurostar is great for wheelchair users.  You can book the cheapest ticket (approx. £39) and travel Business Class as that is the only carriage where wheelchair users can be accommodated.  For an economy fare you get access to the lounge beforehand and a beautiful meal on board with plenty of drinks thrown in.  You also get to bring a carer or a plus one.  Excellent value and a very comfortable way to travel.  https://www.eurostar.com/rw-en/book-wheelchair