[JockoT]

Although there is a minimum speed limit sign in the UK Highway Code, I believe there are only two places where it is used. That is the Mersey Tunnel and the Dartford Tunnel (both 10mph, minimum). In Northern Ireland there is a minimum speed limit of 30 mph on Motorways, but not in the UK, though you could be cited for driving at a speed not commensurate with the traffic flow. Dual carriageways are just normal A roads but with an extra lane in each direction and as such are covered by the same laws as a quiet road in the highlands or islands (apart from a slightly higher speed limit).