First, you are wise to continue with your limit of one British car at a time. Do that. Second, my first Brit car was a 1971 GT6 with an electric overdrive and all my memories of it are positive. It was only a few years old and ran and handled very well indeed. So it left a good impression. The next few cars also did not dampen my enthusiasm for that genre of transport and I have fond memories of my MGB GT and MG Lemon Hundred.
But many decades have passed and now I have a 1970 British sports car which has been the worst car I ever owned. It literally has had an unending stream of issues starting the first day of ownership. As soon as one matter is resolved and corrected, another pops up. It is so consistent as to be unreal. Almost like someone has made it their life purpose to assure that there are troubles. This has gone on for almost three years. I know this vehicle more intimately than I’ve ever known any other car. My theory is that the end of my troubles is near because the machine is simple and finite. It is the only car I’ve owned that literally has got newer the longer I have owned it and my assumption has been that it’s troubles followed the combination of poor previous owner choices and the effects of time. I also assumed that it performed just fine from the factory, so the problems are all correctable. I wish it had been as nice when I bought it as it is now.
My very good experience came from the venerable GT6. My worst car makes me very sympathetic to your experience. I think I have you beat though.