Unenforceable

The government it seems wishing to curry favour with motorists (whilst taxing them to penury) have turned their attention to clockers... (Centre Lane Owners Club) and the maddening driving skills of some people who deem it their god given right to get into a lane on a motorway, drive at ten miles less than the speed limit (at least) and refuse to move out of that lane come hell or high water with a line of traffic tailgating behind them.
Sounds good in theory... in practice, well lets just say that this has the possibility of getting right up a lot of motorists noses.
Telegraph.

New on-the-spot penalties for motorists who hog the middle lane, cut up other drivers or tailgate will be unenforceable with the current numbers of traffic officers, police have warned.
From today, drivers face a £100 fine for these offences as part of a package that will also see people get three points on their licence for careless driving. The fine for using a hand-held mobile while driving will increase to £100 as well.
But the Police Federation suggested the initiative by the Department for Transport (DfT) had failed to take account of the cuts to the policing budget rolled out by the Home Office. Steve White, vice-chairman of the policing body, said: “It’s all very well for the DfT to come up with these new ideas when the Home Office are at the same time cutting the number of police around the country, which means a fall in the number of traffic police.

What they are saying is basically true, at the moment once you spot a traffic cop, you know once you're out of their way you're pretty much clear till the next county. If anything like speed cameras the traffic cops themselves often cause traffic on spotting them to bunch as people slow down to check their speed, even if they are within the law.
Among the offences police are expected to focus on are:
• Driving too close to the vehicle in front
• Failing to give way at a junction (not requiring evasive action by another driver)
• Overtaking and pushing into a queue of traffic
• Being in the wrong lane and pushing into a queue on a roundabout
• Lane discipline, such as needlessly hogging the middle or outside lanes
• Inappropriate speed
• Wheel-spins, handbrake turns and other careless manoeuvres
 All of which actually require a police officer to witness said activities and as I've pointed out above, the likelihood of that is pretty low.
In other words it's bad law as it's pretty unenforceable outside the view of a policeman and is unlikely to be policed by consent as such activities as theft, violence etc where the public can and do report such matters.
Just another revenue raising activity at best...