I have always bought a large proportion of my clothes second hand. When I was a teenager (not in the U.K.) it was largely due to financial reasons. This was before second hand became cool. Anyway, the habit stayed with me and over the years, living in London, my wardrobe has been a mix of second hand (80% I would say), basics from places like Uniqlo and the occasional more expensive new item.
But in the last couple of years or so I have increasingly found very little worth buying in my local charity shops. There are fewer nice things (being sold online maybe?) and what is there is really expensive. Today I had a good look and there were gems like a shrunken Uniqlo jumper for £17 and lots of similar things.