What are the NHS's official policies regarding transsexuals? If they have any, the policies probably at least hint that transsexuals of either variety should get treatment - I very much doubt that it's written out to only include MTFs (this isn't Iran, after all). Look up the 500-page (or however many pages. Random number) version of their policies and see what it says about transsexuals. If it's not specific (and I highly doubt it is), you should be covered to the same degree that MTFs are.
Or do you just mean that the only NHS doctors who treat FTMs on a regular basis are in London? If so, you can be treated by a general practioner who doesn't have FTM experience, so long as he/she's willing to treat you. You'll have to give him/her quite a few pointers, of course.
(sorry for being non-specific. I'm American, so I am zealously guarded by my angelic Republican party from ever experiencing the pure horror that is a public right to health care. It is my patriotic duty to instead pay roughly 95% of my income for a health insurance premium that, should I actually get sick, would chuck me out the window and run screaming from the prospect of ever doling back any of my money for medical care.
Things could be worse. You could live in the only major Western power where half of the politicians are still fighting tooth-and-nail to keep their citizens with empty pockets and miserable health.)