For real winter temperatures, like the kind I imagine you get in the UK, and for long road rides in those conditions, you basically have to choose between using winter cycling gloves with other protection, like poagies made for drop bars, or gloves that can be worn alone but which don't offer the tactile feel of winter cycling gloves, like lobster gloves that have all four fingers in one "claw."

I'm not a road cyclist, but I live in Wisconsin, one of the more northern states in the continental US. One year I used the full-blown winter gloves; thick, fluffy lobster gloves. The second year I used my winter cycling gloves (Castelli, which is a good brand, but the gloves are only warm enough in early-winter conditions) together with Bar Mitt-brand poagies (I do NOT recommend the Bar Mitt-brand poagies). This year I designed my own insulated covers for the Bar Mitts and lined the inside of them with a synthetic fur, which is used without gloves.