>>> However, the Eurostar trains are expecting problems. I believe it is not possible to book trains after 1 Nov at present (but willing to be corrected.
Well, I'm happy to correct you!
I've just searched for trains on the Eurostar site after the planned Brexit date and they're appearing normally.
Further, this is shown there:
"We expect to maintain services on the existing basis, timetable and terms and conditions following Brexit. We are working closely with our station partners, Governments and border authorities on both sides of the Channel to ensure that robust plans are in place for us to continue to operate in either a deal or 'no-deal' scenario"
Source:
https://www.eurostar.com/uk-en/travel-info/service-information/eurostar-travel-updates