Police authorities already tend to turn a blind eye to motorists going at 80mph.

Motorway speed limits could rise to 80mph

Motorway speed limits could rise to 80mph

By Phil Scullion

Motorway speed limits could increase from 70mph to 80mph in a move which has been criticised by road safety campaigners.

Philip Hammond is to announce plans for a consultation on the issue at next week's Conservative party conference.

There could also be a big expansion in the number of 20mph zones in built-up areas under government proposals.

The transport secretary will argue that shorter journeys can help boost business in Britain, although environmental groups are likely to point to higher greenhouse gas emissions as a result of higher speeds.

Road safety campaigners have condemned the potential speed limit increase, saying it will lead to more deaths and serious injuries on Britain's roads.

Ellen Booth of the campaign group Brake said: "The government should be looking to reduce the number of deaths and injuries on our road not putting forward proposals which are likely to increase them.

"We work closely with families of those who have died in car crashes and for every statistic there are real people who are suffering."

In 2009 there were 132 deaths on motorways and the total number of road deaths was 2,222, the lowest since records began.

Mr Hammond has called for a "rigorous cost benefit analysis of speed limits" looking beyond simple safety issues.

He said: "If you took just that view, you would have 10mph limits everywhere. We need to look at the value of safety benefits and the cost in terms of additional journey time.

"It is a bit of a no-brainer that that is how it should be done."

There are also concerns that with the current practice of police and authorities turning a blind eye to most motorists travelling at 80mph, many could now feel permitted to travel at 90mph.

However supporters of raising the limit point to the fact that when 70mph speed limits were introduced in 1964 they coincided with the maximum speed of most cars.

Latest Department for Transport figures show that almost half the cars on Britain's motorways exceeded the 70mph speed limit last year.