Not to pile on, but I'm afraid I'm not sure even Genki (or a textbook of similar quality) would help if he's just going to end up using it in a scattershot way.
Tae Kim's guide is far from spectacular, but if read carefully, certainly it could provide a basic understanding of the basic, fundamental elements of Japanese grammar that the OP still seems to be stuggling with.
I'm not sure where in the UK he lives, or if this is even feasible, but it seems like his best hope would be to find a volunteer Japanese class of sorts, at a community/cultural center or what have you.
It strikes me that if he can find a patient and qualified teacher who can help him get over this initial mental block and understand, on even the simplest level, how Japanese does and doesn't work, perhaps things might "click" somewhat, allowing him to work from there and build upon that foundation.
Back in my grad student/TA days, I would have loved the challenge of trying to work with the OP one-on-one. I'm fairly certain he could benefit from repeated reinforcement/exposure, so that mistaken assumptions don't linger in his head (and even worse, compound each other).