The idea
I would remove elements of the road traffic act restricting the speed on motorways to 70mph. This might have been appropriate when we all drove Austin 1100s and suchlike but with modern vehicles with far better braking systems a limit of 100mph on the longer link motoways outside of the South East where of course congestion limits speeds to about 40mph would be far more appropriate. This would help get the economy moving outside of the South East by getting people from A to B far quicker.
Obvious places for this are the M1 north of Luton except around J23, the M4 west of Reading, the whole M6 except around Birmingham where the M6 toll road would be of higher speed to encourage more people to use it, the M5 in places, the whole M74, most of the M62 and parts of the M8 and M9.
Motorways in the southeast and those with known accident blackspots would have the 70mph or lower retained through signage.
Why is it important?
Business congregates in the South East for the simple reason that the concentration of affluent customers is in the South East. Train links have improved but if you need to carry small quantities of goods or samples, or get to places outside of London, this isn't an option. For someone from Scotland, the journey by car becomes a monotonous 70mph crawl down relatively empty motorways until you get near to London when of course the traffic volume restricts speeds naturally anyway. I accept most people actually do 80mph in this situation but a legal 100mph would knock at least an hour off the journey meaning you arrive fresher and more able to work effectively.