Wow!! You moved from Wales to London. (I know some Irish, Scots, and English and they have told me stories of the Welsh and the Welsh have told me stories of the same)

To the question.

In Oregon, which is really wet, during the fall/winter I wear just a breathable waterproof jacket with lightweight Columbia snow pants. The pants are non-insulated, but breath well enough. The jacket is the same. I compensate for warmth by wearing Underarmor and layers. It also helps to trap the sweat.