Dave,
Dont give up, and more importantly, don't put up with such crap.
Instructors like this are all too common in the UK, and for the most part they are egotisical cowards who are fond of their own voice, and are not worthy of the profession they purport to represent. You'll probably find that the people you've been unfortunate enough to be involved with are part timers, or old farts, who are only interested in keeping their licence up for minimal or no flying pay, you'd probably find they'd change their attitudes if you put them up against the wall and gave them a good twatting (an unorthodox yet proven solution).
Go somewhere else and realise your ambitions, it may cost you a bit more, but it'll be well worth it for your own satisfaction and self esteem.