Those AREN'T walk in clinics like they have in the States and the Republic of Ireland!! In those countries, walk-in clinics are free charitable clinics for people without health insurance, who would otherwise get no basic healthcare. The clinics you mean in the UK are run by the NHS, and are something between a GP surgery and wherever they stick people in hospitals that aren't critical enough for the A&E department. As they are NHS run they WOULD NOT EVER provide blood tests for or finasteride for hair loss, even if you waved money in their faces! Find me ONE example of an individual IN THE UK who has attended a walk in clinic and gotten finasteride for hair loss AND the relevant blood tests to monitor progress, and I will PayPal you fifty quid.
Secondly, I don't have any of those NHS clinics in my area as I don't live in London or a big city.