The stopping distance will depend on your attention, the road surface, the weather conditions and your vehicle.
Stopping distances. Drive at a speed that will allow you to stop well within the distance you can see to be clear.
If you have to stop in a tunnel, leave at least a 5-metre gap between you and the vehicle in front.
If your vehicle is fitted with anti-lock brakes, you should follow the advice given in the vehicle handbook. However, in the case of an emergency, apply the footbrake firmly; do not release the pressure until the vehicle has slowed to the desired speed. The ABS should ensure that steering control will be retained, but do not assume that a vehicle with ABS will stop in a shorter distance.
Keep a Safe Following Distance - The Highway Code recommends you keep AT LEAST a 2 second gap from the car in front (in good dry road conditions). To judge a 2 second gap you wait for the car in front to pass a fixed object (for example a lamp post or road sign) and then count 2 seconds, this can be done by saying the phrase "only a fool brakes the two second rule" (which takes 2 seconds to say), if you can say the phrase before reaching the fixed object then you are a safe distance behind, if you can't say the phrase they increase your following distance (i.e. drop further back from the car in front). In wet conditions AT LEAST a 4 second gap should be kept, and in icy conditions AT LEAST a 20 second gap should be kept.
You MUST NOT exceed the maximum speed limits for the road and for your vehicle. A speed limit of 30 mph (48 km/h) generally applies to all roads with street lights (excluding motorways) unless signs show otherwise.
Cars & motorcycles (including car derived vans up to 2 tonnes maximum laden weight)
30mph (48km) = Build up area
60mph(96km) = Single Carriageways
70mph (112km) = Dual Carriageways
70mph (112km) = Motorway's
Locally set speed limits
20mph (32km) = passing schools
50 mph (80 km/h) on single carriageways with known hazards