I was terrified of driving on motorways, so got a steady reliable friend to ride with me. He drove for a couple of junctions, talking to me about how he was driving, then we swopped over. If I couldn't cope, I intended him to take over.
Driving was so awful that I was hyperventilating, my fingertips were going numb and my vision was starting to get fuzzy. I realised that I would have to stop unless I got myself under control PDQ.
Then I realised tat I had been pootling along conservatively in the lh lane, with no problems whatsoever. I didn't need to overtake if I didn't want to. I'd passed a junction and allowed the traffic to merge without having to change lanes. In other words I was doing fine. A few deep slow breaths and I was physically OK as well.
I hated m/way driving for a long time, but forced myself to do it from time to time to make sure that the terror didn't reset itself. I don't think I overtook on a motorway for at least five or ten years! You must bear in mind that you don't have to drive like everyone else, you can pootle along at 60 in the LH lane, slow down to let traffic merge, and not be pressured into doing anything you feel unsafe with.
Now that I live outside London, I have had to get used to m/way driving, and the more I do it the more relaxed I am about it.