I’m not one for wearing suit jackets with jeans – I end up looking like Jeremy Clarkson rather than the suave-but-casual urban lad I imagine I am. But I might give the look another go if I can get my hands on this Monsoon blazer (£70) which has an informal cut and that "slept in" appearance.
The blazer would look great with just a black t-shirt underneath and a battered pair of jeans or charcoal slacks. It would look even better with an old trilby. Then you could pretend you’re some old jazz saxophonist who’s just finished a set at 6am in some little dive somewhere. That’s what I’d do anyway. Because I’m a bit strange like that.