I have clamydia or ghonneria and want it treated. would a drop in sex clinic do this, or do i see my gp?

I'd choose clinic: In the UK, you'll almost never go wrong with a NHS genitourinary medicine (GUM) clinic, most of which operate primarily on a drop-in basis (I think). You'll have guaranteed expertise and sensitivity to any sexual lifestyle. Your GP also might provide excellent care, but the STD expertise of GPs (in UK or any other country) is all over the place -- some excellent, others with poor understanding.