Same here, for my 15 minute commute. Regular clothes, with outer layers depending on weather. I don't bother with rain pants up to a light drizzle. Wool (pants and/or sweaters, ...er "jumpers" to you in the UK!) also will tolerate a bit of damp, keep you warm, and breathe well. Many outdoor companies make softshell jackets that are pretty water resistant and don't scream "cyclist." I add hi-viz and reflectivity if needed with a Sam Browne belt or reflective straps. I also wear Underarmor to mitigate chafing and manage moisture.