A Tory MP said that the erection of 70mph speed cameras along the motorway in his constituency was for Labour's " politically correct, money-making reasons".
James Gray, Conservative MP for North Wiltshire, said this was his "gut instinct" on hearing that Wiltshire and Swindon's Safety Camera Partnership are to install cameras from junctions 14 - Hungerford - to 18 - Bath - of the M4.
From lunchtime today motorists exceeding the limit will be fined £60 and will receive three penalty points on their licences.
The cameras are being set to photograph cars going 79mph or more for safety reasons.
Mr Gray said that if the Tories are voted into power, they will raise the speed limit on motorways to 80mph.
"The M4 is virtually straight between those junctions," said Mr Gray.
"I cannot think of any dangerous stretches. I am not aware of any safety reason why cameras should be there."