I am also very glad I read this thread. I passed my test years ago and then had a big gap before driving then I decided to return to driving when trailing around with two young children on public transport became too much. Though still use public transport too of course.
At first I felt panicky about driving locally and it was a big deal to go around the roundabout at the end of the road. I do live in London though so perhaps that was quite reasonable.
I had an old car at first which didn't help my confidence. Then I got a newer car and this helped enormously. Then the next challenge was to drive under the Blackwall tunnel or Limehouse link for example. Now I am fine whizzing around London and would even go so far as to say I really enjoy it.
Along the way I saw a hypnotherapist and also read a book by Paul McKenna. Neither had an immediate effect but I do think they helped in the long term as eventually I felt a definitive change in my mindset. (This technique has also worked with food for me)
Now (and to get to the point) I have driven four times the 80 miles to my parents in the East of England and whilst I can't say I really enjoy it and find it quite scary and often panicky (I could feel that adrenalin rushing through me) I am forcing myself to do it. I find what helps me is very lould high energy music, chewing gum and trying consciously to relax. Also I was more relaxed when I made a spur of the minute decision to drive there rather than thinking about it beforehand.
However when I hit the suburbs of outer London on the way home I can feel myself become much more relaxed. But I hope that with practice it will get better and I will feel the same way about the motorway driving as urban driving which I now love. What I don't like about the motorway is the speed, the openness of it all and the feeling you can't get off.
Good luck with it all I do have some awareness of how you feel.