What are the exact travel dates and trains involved? We'll be able to help better from there.

The Eurostar is indeed quite expensive... you could look at the Harwich - Hoek van Holland daytime/overnight ferry one-way. 20-30% discount with Interrail and cool experience overall.

Then crossing Germany is much cheaper (3-4.90€ per person) but punctuality isn't great. Don't expect to make 7 min connections. You can always plan with longer stopovers in the first place or simply take the next available train as you go.

That's the good thing about Germany: trains are frequent. Interrail gives you flexibility too.

The Interrail booking interface is confusing, unreliable and often wrong. You should book through the railway companies whenever possible. Have a look at https://www.seat61.com/interrail-and-eurail-reservations.htm

About the SJ (or Snälltåget) night train, hard to say without more details. Maybe the website is under maintenance right now as that shouldn't happen.

(Feel free to add anything, I'll answer tomorrow morning.)

There are 2 night trains running between Sweden and Germany. SJ Euronight, which has seats, couchettes and sleeper, and Snälltåget, which has seats and couchettes. 

What dates do you want to travel?

Thanks for the replies - I am going out on 15th August - and travelling back overnight on evening of 31 August - 1 September.

I have just found out that there is no way of making reservations on the London to Cologne leg of the journey as its all booked up so will explore going via Hoek van Holland. Its that or cutting our losses and getting the plane - I really don’t want to fly but the current tally for the pass, reservations and hotel stops for a couple of nights en route is coming in at close 2000 - without even counting in the holiday bit! 

Mmmm all trains from London to Brussels are available to me on 15th August (screenshot attached). Then you can take the ICE to Cologne: running every 2 hours, mandatory reservations in summer but loads of space at the moment.

Feel free to let us know what doesn't work.

The London to Brussels leg was working but not the onward journey to Cologne - maybe I did something wrong? 

ah - its because when i tried doing it in one trip - London to Hamburg it gave me trains going via Dusseldorf instead of Cologne!

Problem solved - thank you. Though not sure i can afford all the reservation fees…. but thats a different issue

Yeah often better to split bookings.

Eurostar is definitely the most expensive (30€ pp). The rest should be much more manageable at 3-5€ pp. German reservations should be max 9.80€ for the whole family for the whole journey. Use DB Navigator app or website: there’s even a seat map.

The night train could be a bit expensive but remember that you’re saving a night accommodation in Scandinavia!

Have some margin when crossing the Ruhr area as delays are common. Cologne is likely the best place to change towards Hamburg, looks like you get 50 min which is ideal. Time for a little bit shopping too.

You could also avoid that area altogether by going via Amsterdam - Osnabrück (either way).

Thank you - really helpful!