Obviously no direct trains and you would have quite a journey to get to Germany, I assume via Sweden and Denmark. From Hamburg you would need to get to a Eurostar station best Brussels then to London.

Do you know if there are any ferries I could take from Norway to the UK?

Denk het wel-daarvoor is er google-dan komen er 12345 sites die alle directferries etc tonen. Maar er is de laatste tijd nogal wat beweging daarmee-zeer hoge brandstofkosten en ook GB na de Brexit=veel meer ergernis bij inreis etc. Was er altijd vanaf Bergen/NO. Maar behoorlijke lange reis=behoorlijk duur en valt helemaal buiten passen. Tiepies van die dingen dat je toch maar naar die plane gaat denken. Ook al omdat vrij veel ferries tegenwoordig ook nog enkel pax met auto/motor ed willen meenemen. Heeft mede te maken met de GB angst voor illegals.

ALS er toch nog wat is wat je aanstaat (mogelijk bvb ook nog vanaf Göteborg/SE) dan best direkt bij die mij. boeken en niet via die tussen-sites. Dan kan je ook beter alle geboden discounts zien.

I travelled on the ship (overnight) from Oslo to Copenhagen and then spent a few days there. Took a train to Cologne. Stayed overnight and then to Bruxelles and Eurostar to London. 

There's also a ferry from Eemshaven to Kristiansand. Both ferry ports are next to a railway station.

Where are you leaving from, in Norway?

Hirsthals (north of Denmark) has also multiple ferry connections to Norway and is quite okay by train.

And if you really want to go from the beaten track, but unfortunately now only an option by car:

From Ghent (BE) it is sometimes possible to book a place as a passenger on a freight ship, that goes to Göteborg, from where you have train (and bus) connections to Norway (or the other way around is also possible). Once a week there’s a ship to/from Brevik (No) (close to Porsgrunn, with good connections to Oslo via Vestfoldbanen).

It takes a long time, but so does the train or any other transport possibility than plane. And you usually need overnight facilities. The harbours are also not that accessible. But pre covid you could do it with bike or as a foot pax. Let’s hope it returns, it was very convenient to get from the north from my hometown ).

Travelling over land to Norway takes time, but is very enjoyable and adventurous whatever the option.