Agree with what others above have said, but for me, the stand out phrase in the OP's post is "but I am very assertive". Perhaps have that on your gravestone. Just give way and let the i**** go on their way.

I'm familiar with the A34. It's an awful two lane dual carriageway, most of which is NSL. At busy times lane 1 is HGV and lane 2 is other traffic trying to do 70mph plus and getting frustrated should an HGV pull out into lane 2. A road I try to avoid.

And I thought it was just me that avoided the A34, but in my case because of 'elephant racing'. I prefer to use the A420 from Oxford to the M4.

Let aggressive drivers have their way. They will eventually meet someone more aggressive or stupid and get their.comeuppance.

When I'm doing a true 70 on a dual carriageway, I somewhat resent moving out of the way of 'Transits' (I'm including all makes) whose drivers seem not to know their own limit and want to break mine

Surely a contradiction here?.

Also, if you can get out of their way, surely you don't need to be in the overtaking lane?.

I was once on a speed awareness course with a chap who had been driving a van for 20 years and swore he had no idea that his van was limited to 50 and 60 rather than 60 and 70 on single/dual carriageways.

This doesn't surprise me. When I first started cleaning windows, I looked into the speed limits for vans. It seemed pretty vague unless you were driving a van with a GVW of more than 2 tonnes. Now that everything is lumped into the LCV category, it is clearer, though not if you are driving a pickup. Where you may be subject to LCV speed limits, or you may be subject to the same limits as a car. Can't remember exactly what determines the category a pickup falls into, but this is surely an unnecessary confusion?.

No contradiction, and your reasoning is faulty. I move when reasonably able to do so, but I do feel some frustration that very little seems to happen either in enforcement or education about the enormous number of such vehicles doing well over 70mph every day. I'm often on the A421 between MK and the A1 when it happens, a busy road where one can spend a lot of time in lane 2 passing lorries. Often (and I mean often - I can be overtaken by half a dozen or more on a single journey) a van will close up behind me, so I extract myself at the earliest opportunity, even if it requires dropping my speed to join slower traffic in lane 1.

My resentment is mainly directed at the lack of any visible attempts to deal with them. This road is in Bedfordshire, where the Chief Constable notoriously wanted to remove all speed limit tolerance a while back. If he wants to dish out tickets he should start with vans that are limited to 60, tailgating at 80 and not infrequently driven by people with a phone clapped to their lughole.

We can't necessarily help being irritated by these people but we can control our response, is the point.