You should try driving parts of the M25 in the early hours.
Invariably at least one idiot camped out in lane 3, 4, 5 or 6 doing less than 70, the only worse thing being the Highways Agency posting random mandatory 40, 30 or 20mph limits for no reason (once all on the same gantry....)
What to do? well the answer in many cases is that many people will not undertake, so you end up with a near empty motorway banjaxed by one moron.
The sitiation is unacceptable as it stands.
First off, there is currently no absolute law against undertaking. That was abolished by the RTA 1972, which replaced a number of specific offences with a more generic (and therefore subjective) offence of careless or inconsiderate driving.
It is that subjectivity that causes endless debate and a lot of nonsense, not least because the CPS inevitably give things their own spin by choosing some selve serving examples
Careless/inconsiderate driving
"As with dangerous driving, the circumstances of every case of careless or inconsiderate driving will be unique and we will consider these before reaching a decision as to the appropriate level of charge. "
All well and good so far.
However:
"There are decided cases that provide some guidance about the driving that the courts will regard as careless or inconsiderate and the following examples are typical of what we are likely to regard as careless or inconsiderate driving:
Careless driving
overtaking on the inside;
driving inappropriately close to another vehicle;
inadvertently driving through a red light;
emerging from a side road into the path of another vehicle;
tuning a car radio;
using a hand-held mobile phone or other hand-held electronic equipment where the driver was avoidably distracted by that use;
selecting and lighting a cigarette or similar where the driver was avoidably distracted by that use.
Inconsiderate driving
flashing of lights to force other drivers in front to give way;
misuse of any lane to avoid queuing or gain some other advantage over other drivers;
unnecessarily remaining in an overtaking lane;
unnecessarily slow driving or braking without good cause;
driving with un-dipped headlights which dazzle oncoming drivers;
driving through a puddle causing pedestrians to be splashed;
driving a bus in such a way as to alarm passengers"
Ah right.
So just form your own view on what to do in the circumstances presented because, after all,
"There are decided cases that provide some guidance about the driving that the courts will regard as careless or inconsiderate and the following examples are typical of what we are likely to regard as careless or inconsiderate driving."
The "we" in all that is the CPS & hence Plod. Anybody wants to have a go at me for undertaking in normal circumstances with no aggrevational intent off they go: see you in court.
http://www.cps.gov.uk/publications/prosecution/pbd_policy.html#_26