He's 32.
He's been with you for 5 years.
Until meeting you, at 27, he was content to live with his parents and do an admin job.
It took him more than 4 years after meeting you (when he was 31) to decide that he wanted to do IT.
It's now going to take him 6 years to qualify, so he'll be 37-38?
You have already nearly halved your earning power because of him:
"I was working at a law firm long hours often getting home 11pm or later and earning £60K. He was unhappy with the hours I worked so I agreed to look for something with better hours and accepted the council job earning 35K."
And now he wants you to compromise your career even more by moving away from London - not to another city like Birmingham or Manchester or Bristol where you might have some opportunities, but to a small town in Wales.
Basically he wants to move back in with his parents, where he was happy for 27 years of his life, and he wants you to fit in with that.
I wouldn't do that in a million years. I don't think you're even compatible. I understand that you love him, and at 35 your biological clock is ticking, but I don't think those are good enough reasons to stay with him. Your life goals are too different.
Also...
"She’s always treated me with kindness but the last time I was there she did say I was being unreasonable and that she can’t understand why I won’t move to Wales and move in with them until we have jobs because ‘family is most important thing’"
Be careful. Be very very careful. Marrying a mummy's boy can be a recipe for disaster if he's not willing to cut the apron strings. It will be him and mummy against you.
"The only other option is him doing the degree full-time to get done quicker but I don’t want that I think it’s important for him to contribute however little."
I have to say it does seem crazy to drag it out over 6 years while he's only doing a low paid part time admin job. It would make more financial sense for him to do the IT degree as quickly as possible and then hopefully get a better paid full time job at the end of it. There are plenty of students doing full time courses and part time jobs on top. What's to stop him doing that? Even if the job is just a few hours at evening/weekend? But then he didn't want you working long hours, did he, so he won't want to do that either.
If he actually doesn't care about his career and wants to be a SAHD, then the IT degree is basically just a hobby. And you'll need to live where you can earn enough to support the whole family.