It does however mention matching speed which assumes an attempt to enter a moving gap - which has to be there in the first place. If by not creating that gap (by simply easing off the throttle) traffic on the slip road is forced to stop then IMO a dangerous situation is created. Forcing a vehicle to enter the motorway from a standing start just so you don't suffer the minor inconvenience caused by creating a gap is discourteous at the very least. Not all common sense activities have to be mentioned in the Highway Code - a bit like allowing someone to join the road you are on from a side road. And I do understand about HGV problems - although in my experience those drivers tend to be pretty good at spotting in advance vehicles approaching from the slip road.The Highway Code says: -
- give priority to traffic already on the motorway
- check the traffic on the motorway and match your speed to fit safely into the traffic flow in the left-hand lane
So nothing there about people already on the motorway easing off. There always used to be a rule that you should never cause another vehicle to change speed or direction in any aspect of driving.