It’s valid on the Elizabeth Line to Heathrow, but not the tube or Heathrow Express.

For whether it’s good value you have to do the maths. Compare the price of the pass + compulsory reservations, with the cost of individual tickets.

I think it’s unlikely a pass would be good value for you, but if your children are under 12, it’s possible, only if the cash prices on Eurostar are high.

You can check Eurostar prices on their website. They have a special destination of ‘any Belgian Station’ which would save you having to buy a separate ticket to Bruges, if your onward connection is within 24 hours. In any case, the ticket won’t be expensive if you have to buy it.

Individual ticket from London to Brussels is 260 on December 21. Seems really expensive.

That’s the Saturday before Christmas. It’s not going to be cheap.

In any case, there are currently no passholder fares available on the 21st to Brussels, so a railpass is no good (unless availability suddenly appears, but I don’t think that’s likely).

If you have to travel on the 21st, you’re looking at an expensive train or flight. You might want to look into flights to nearby destinations, or even the ferry.

Either way crossing the Channel is going to be very expensive as ralderton said.

(On 21th December one morning London-Paris Eurostar would have availability for 5 (07:31-10:50 incl. 1h time difference) → 38€ 1st class passholder fare. Perhaps have lunch in Paris before heading back north to Lille (20€ for the high-speed train) and then Bruges. But it’s a bit stupid…)

Personally I’d rather get the last tickets on the direct London-Bruges Flixbus (133€ per person). The journey takes 7.5 hours overall but a good time will be spent outside the bus for border checks and then onboard the ferry. Seems the best choice to me! Book ASAP.

Train tickets within Belgium are cheap, unlimited. You can buy them on the day, don’t worry about that.

Now remains the leg back to London. On which day would it be? Note that pretty much nothing is running in the UK on 25th December.

EDIT: on 24th and 25th December there is a decently priced (55-60€) Flixbus from Bruges to London leaving at midday. Again, seems ideal to me. This one even takes the Channel Tunnel onboard a train for a fun experience! ;)

Feel free to ask anything.