As others have mentioned who is going to enforce this? there is a distinct lack of police presence anywhere either on foot or in cars, I drove down to Milton Keynes yesterday in torrential rain and it's fair to say that it was probably the worst rain I have ever driven in on a motorway however these adverse conditions didn't seem to affect others who continued there journey at unabated speed,some with mobiles in hand quite happily tailgating others whilst making an important call
IMHO driving standards and people's behaviour behind the wheel seems to have significantly dropped in the last 10-15 years, tailgating, boy racers in there souped up Corsa's racing each other, mums in there Chelsea tractors on the school run getting there oh so precious offspring to school and oafs in Audi's, the list goes on and on
There is no deterrent, there are no police so the government can increase the punishment but the idiots perpetrating this madness know that they can get away with it, it's the attitude of 'Meh'
Here's a good idea though to combat one of my pet hates, idiots in cars passing to close either deliberately or because they just don't realise or are just plain thick, although I still don't know where they will find the manpower to carry it out though...