Info here....
Applies to dual carriages and motorways ...60mph is still the limit for single carriageways....
The 70mph motorway speed limit was introduced in 1965 and has been the subject of Government review on more than one occasion. The last review was carried out in 2001. This review looked at the possible effects of increasing the motorway speed limit to 80mph. It concluded that raising the motorway speed limit would run too great a risk of increasing accidents and casualties. In addition any increase in speed limit would result in higher emissions of CO2 and oxides of nitrogen and generate more noise.