Finding a specialist in the uk

A GOOD FRIEND OF MINE HAS SUFFERED FOR SOME 5 YEARS, AND ALTHOUGH HIS GP HAS TRIED HIS BEST I THINK HIS LACK OF KNOWLEDGE OF THE CONDITION HAS HAMPERED PROGRESS.
CAN ANYONE HELP WITH A SPECIALIST IN THE UK?
I BELEIVE THERE IS ONE IN HARLEY STREET LONDON BUT I WOULD BE GRATEFULL FOR ANY HELP ON LIVING WITH AND TREATING THE CONDITION.

BEST REGARDS PAUL