As you most likely very well know the one and only train running under the channel to this funny island in the NorthSea is this €*-from Paris or from BRUssel(some come from Ams). They are fully booked for passes-seats the coming week. There has never ever been a night train-well-for railfans-there was via a ferry a century ago. In fact many trains are completely fully booked-many cancelled flites and a sudden boom in travel post-covid, with staff shortages and the strike here+there are the reason. On the site of b-rail one can check when there are seats for passholders from either start.

YOu can certainly-perhaps not on the direct TGV-but with some more changes or slower-reach the channel-but then next surprise-the ferries do NOT take foot pax for now. The only one that may is the Hook of Holland (NL) to Harwich Stena line.

The only viable ALT are: fly-whatever flite you can get from an airport moreorless on the way-as you likely know RYAN is most often the cheapest but not best-check where they fly from to LST/LGW etc-or maybe even closer to your home.

Then its BUS-Flix-with same handling-they mostly go via ferry and take thus much longer-but also overnite (with all the changes not much sleep to expect).

On this forum we see every day loads of Brits who planned their eco-green holiday trip on the trains and had to face this same disappointment as first hurdle.

Do you have a 1st or 2nd class pass? 

Your big problem will be to cross the Channel if you want to do it by train. I doubt that there will be any possibilities at all. 

There is a limited number of pass holder seats on the Eurostar and on popular departures and during high season those sell out weeks, and sometimes months in advance.

The best place to see the availability of passholder seats on the Eurostar is 

https://www.b-europe.com/EN/Booking/Pass#TravelWish

If you spent less time making snide national insults and smart-arse comments to people you would perhaps stop giving as much bad information out. This is at least the third time you have stated this despite the fact I already corrected you on it a few days ago.

Once again: P&O ferries offer 2-4 daily foot passenger crossings each way Dover - Calais, times and bookings on their website. https://www.poferries.com/en#route

My experience is that @mcadv needs at least three reminders before he can remember information. Yes, that's annoying.

It is also worth noting that North Sea Ferries are still operating a daily overnight service from Rotterdam to Hull. (Owned by P and O Ferries). Foot passengers welcomed.

Also several ferries operate from Normandy and Brittany to Southern England.