I would've thought you could get it at Holland & Barrett
I got it at Beanfreaks in Cardiff recently, but that was because I happened to be in Cardiff and that was the place where the crazy herbal remedy guy recommended it to me.

I'll have a quick look online and see whether you can find the right stuff on the high street.

edit: not quite what I use, but will probably do the job
www.hollandandbarrett.com/pages/product_detail.asp?pid=261&prodid=24

edit2: this is what I use
www.healthstore.uk.com/p449457/swiss-herbal-remedies-valerian-tincture-50ml.html
( Vipros. clever got me this far, then tricky got me in, Wed 12 Jan 2011, 9:44, 1 reply, 15 years ago)

thanks very much
I'll get some.
( SteveFrench Cardio is for homo's. do you even lift bro?, Wed 12 Jan 2011, 9:55, Reply)