As a staple wardrobe item the basic men's sweatshirt is underrated. It works like a classic tee - goes with everything, comfortable, relaxed but applicably smart. Except the sweatshirt will also keep you warm when the weather is not quite on side (London: that'll be most of the time then).
Street Style Sweatshirt Inspiration
As the cooler nights draw in, not quite ready to give in to thicker knits and winter coats, consider the humble sweatshirt. Easily transportable as a spare layer with minimal creasing (roll, don't fold) and slim enough to fit under a jacket. Or you could give the jacket to your girlfriend/boyfriend/date/mate when they get cold. And let your generosity (and your sweatshirt) make you feel all warm inside. Or just smug.