With the new H&K shop and new prices I won't be buying any.
T&A are superb, with a price to match. H&H are I think a very good compromise between the top end and the 4 for a hundred mob. Of the latter, I actually think T M Lewin are very reasonable. Yes, it is mass produced in some Far East slave factory, but at £25 a go they're perfectly OK.
I'm surprised though that so few people have suggested Budd. Granted, their website is a joke (although if you know the firm that sort of thing really is part of their charm) but the shirts are wonderful. The full price standard poplin shirt is £135, and whilst that is objectively a lot of money, you do get exceptional quality for that money.