Thank you for all your suggestions. I have emailed a local travel agent and she is ringing me today at 12 to talk about what might be possible. She said that they can arrange a coach to the ship pickup point in Southampton, so that is good to know - a lot will depend on the cost of course.
I am not sure about all this as I am not a cruise "type" - don't like posh food or entertainments or dressing up really - my ideal holiday (if I were not on my own or with my limited mobility) would be to go independently and stay somewhere in the middle of nowhere in peace and beauty. Don't misunderstand me, I am very gregarious and love meeting people, but also love the peace of nature. I sound like a snooty cow, but OH and I would never have chosen a cruise, but I would really like to see the fjords and cannot think how else I might do this.
Thanks for all your help. I'll let you know how I get on.