I love these threads. Make me feel so fucking dapper
Basics: M&S for pants & socks, Banana Republic for t-shirts, Uniqlo/Gap for jumpers, hoodies.
Shirts: Urban Outfitters for casual, wherever on Jermyn Street is having a sale for smart/work (Charles Tyrwhitt, Thomas Pink for preference)
Jeans: Carharrt or G-Star. Well made.
Shoes: Size? for trainers, Schuh for shoes.
Having said all that, I almost shop by default - there are many more places that I don't shop - H&M, Primark because they're tacky disposable shit, TKMaxx because I've genuinely never found one thing I wanted to buy and shopping there is like root canal work, French Connection and Zara are overpriced for what they are, Levis are terrible quality these days, and anywhere with big tacky brand names emblazoned on them might as well piss off...
Oh, other good places are Nigel Hall - not cheap, but stylish, understated and interesting, and Libertys for ideas. Designer outlets like Bicester are also good for big purchases.