Here is a bit of knowledge that you might find interesting and it is something I have come to realise from talking with many in this and other movements.
It IS, for me and always has been an innate thing, I have always bucked against inequalities or stupid rules. My journey in this started by going through scenarios that reflected the problem, much like you are doing now.
However, after being with and meeting many people who are knowledgeable in these things, one thing comes to the fore more than anything else.
Common sense, I am not being flippant when I say this, it IS a fact.
There are two sides to this area of challenge, one is to be in touch with ones own innate common sense and the second is to be able to communicate your thoughts in a way that is understandable to your audience. In your case it is the DVLA and there are many documents that would be of use but you have to be able to assimilate the thought and language behind them for them to be any use.
What I suggest by way of helping out on this is to ask that you consider your position.
* - Every action has an equal and opposite reaction; there may be consequences - First understand these before you continue.
* - Being educated is not a necessity; applying what you know, no matter how much, to your problem, this will start a sequence of events that will solve the problem. Not being able to speak or communicate lawful or legal arguments should not stop you from communicating what you know or how you feel.
* - Learn to be more communicative, in a language that the other party understands.
* - Be proactive as opposed to reactive.
* - At this time only research that which is the problem: What do you know about the ACT or statute that you are fighting?
This being the case you will have a better chance of success, however as I know from what you have written, you are not that 'read' so for the time being use your common sense and write it in a way that supports your case and one that they will understand, with the knowledge that there may be consequences.
How to overcome consequences is easy really, just imagine for a moment only, what will happen if you fail and accept it. The FEAR of it disappears almost instantly.
Do not be overwhelmed by the vast amount of affidavits or notices because all these are for specific incidences, some will fit and others won't. If it feels right and you understand it then use it but make it yours first.
In brief just imagine you are stood toe to toe with the ARSE at the DVLA and argue your point, put down your points and let them have it. Once it is out in their domain they will counter it, do the same with their response without being too monotonous and send it back.
For there to be any controversy they have to back up their argument with solid and reasonable facts, if they cannot and just reverting to bullying you can make it clear that their argument is baseless.
That said the other option is to just keep sending the stuff back NO CONTRACT and sit it out.
Maybe my thoughts are not too helpful, but I thought I would just give a different slant on it to get you juices flowing. Hope it helps.
I am not known for being brief

You want to see some of the stuff I have written to the arses, I am sure they stop at the first because they are so inundated they think 'what the hell, this person is a crazy person'.
I am however a lover of the language so I can be precise and to the point when required to.
FUCK OFF usually works but is not advisable in this case.
Namaste, rev;