I was lucky, when I moved there was no Part P. However I never intended the move, it was a gradual sidewards step, started as an apprentice motor vehicle and bridge builder engineering apprenticeship for the local council, found I did well at auto electrics and specialised in auto electrics, and this resulted in my repairing portable traffic lights, SLD pumps wanted some one to repair their traffic lights and were willing to train me in pump repair, I went to work in Algeria as an auto electrician but found myself doing any electrical work, so by 1980 I was doing more work on 220/380 volt than 12/24 volt. Having worked on heavy plant batching plants etc, I found my skills were in demand, by 2000 I decided I needed the paper qualifications and did a 6,12,6 week set of night classes to get 16th edition, inspection and testing and PAT testing. But to be frank my skills at PLC programming resulted in little problem finding work, I did do the odd house bashing but the Part P law stopped that, looked at getting the qualifications for domestic work, but took a degree in electrical and electronic engineering instead. Working in Hong Kong and Falklands I had always been considered as the engineer, but sorry to say my maths was not good enough, imaginary numbers were OK, but calculus I found a problem, and realised I was not going to go over level 5 without a lot more maths, then the funding changed so education stopped.
It does I know seem daft to need to learn imaginary numbers and calculus, as a domestic electrician is unlikely to need them, but the exams for domestic and industrial are the same, so boolean logic may not be used with domestic but you still need it to pass exams, so my son also became an electrical engineer, but he had studied maths in Uni before he started as an electrician, and as an auto electrician I had also been taught maths.
Through my education I have started early enough to be shown how to use steam tables, in the early 70's tried for a HNC but girls got in the way, but at Uni be it motor vehicle, avionic, sound, or electronic engineering we were taught the same maths, so swapping from one engineering trade to another you already know the maths, so a side move is not that hard, but if the job you had before did not involve maths then going to be rather hard.
As to collage courses I was invited to join one to see if I thought it would help, I could not believe the level of education of school levers, where they questioned if mercury, silver, steel, and gold were conductors. So your taught as if a 12 year old, so 10 hours in collage and taught 3 hours worth of real knowledge.
Not the kids fault, I wanted 'A' level maths, so one course was £100+ and three courses were £10 so did three, so did digital photography and physics as easy options, the wiring digram given in the book for physics for a fluorescent lamp completely missed out the ballast. So they are taught wrong in school and collage to start with, and often harder to unlearn incorrect things than if never taught, find this with electricians doing 17th edition when rules change, today 18th edition.
The problem is you need to learn to be an electrician, not simply a domestic electrician, even if you never work on a three phase supply, you still need to know about how it works to pass exams, and I got it wrong a few times, asked can you work with logs I said yes, I had used log tables since being 12 years old, but that was not what was meant by working with logs.