The idea
The 70 mph motorway limit is a relic of the past. Introduced in 1965 when cars lacked the modern safety features that almost every car on Britain's roads today have. Today most drivers ignore the limit anyway, so why not scrap it completely? At the very least it should be raised.
The autobahn system in which an advisory speed limit of 80 mph is set is very effective and there is no noticeable difference in casualties between German autobahns and British motorways. The fact is for many days of the year it is perfectly safe for a vehicle to travel at speeds greater than 70 mph. And for those days where it isn't? Well I'm sure the British public have the ability to exercise some degree of common sense.
Why is it important?
The 70 mph motorway limit is out of date and ineffective. Cars can safely travel at speeds much greater than 70mph. In addition the public is much more used to motorway driving now than they were in 1965 when the ban was introduced. Also, back when it was introduced the 70 limit represented 80% of an average car's top speed. Nowadays this figure is closer to 50%.