my advice for obtaining legitimate Finasteride in the UK:
1- BY FAR the cheapest way is to ask your GP (or dermatologist/hair doctor if you have one) for a
private (not NHS) prescription for generic Finasteride 5mg (not Propecia). Then you split each pill into fifths and take a segment a day. This works out at about £5 for a 9 month supply. The only problem is that some GPs are unwilling or flat out refuse to prescribe the generic 5mg because it's not technically meant for Male Pattern Baldness, even though it's exactly the same drug as Propecia, just a different dosage. So just a BS ***-covering reason really. If you really can't persuade your doctor, you could try to find another one who is more reasonable.
2 -
http://ukfinasteride.info/ a prescription site that sells legitimate generic Finasteride 5mg and 1mg - it's prescribed by genuine British doctor with a GMC number. A little Pricy though.
3 - Join Boots hair retention scheme where they will prescribe you Propecia (and probably try to sell you other stuff like Minoxidil as well). Or ask your GP for branded Propecia. This is probably the most expensive way to obtain it.
wherever you get your Finasteride from make sure you consult with your Doctor before you start taking it!
EDIT:
I would also advise reading Spex's advice on his website:
http://spexhair.com/cheap-uk-proscar-prescriptions/