I'll confess I'm struggling a bit with some of this Andy, but that's probably my failure to grasp the gist of what you've written, more than anything else.
I think I'm correct in my understanding that you're saying that in early 1945, your dad & his REME team were tasked with collecting German armour, presumably so that it could be looked at by the 'boffins' to see if anything could be learned from the designs? I think this is fairly well documented, even to the extent of the British building Panthers & Jagdpanthers after the war to evaluate them (several of which still exist in various museums/collections). I wasn't aware there was any particular 'competition' or secrecy over this between us & the Americans, however, so that's interesting to read.
When you talk about the post-war meeting your dad had, and the subsequent mission to bury "a lot of tanks", though, you say it "appeared to be a cover up from the first operation back in 45", so are you saying that the tanks that were buried were actually German? Also the tank ID plates you mention - are they from the collected German tanks or from something else?
Finally, when you mention that Churchill had amassed a secret private arsenal of weapons in the years running up to the start of the war, and that "nobody ever asked him where they came from when he pulled them out of the bag in 1940" - what weapons are we talking about here? I believe the army in particular was still in the process of (legitimate government-sponsored) rearming at the time of the invasion of France & the Low Countries, and after Dunkirk was quite frankly 'on the bones of its a*se'! Apart from Winston probably having a hand in securing arms supplies from the US & Canada, etc., I wasn't aware that anything was 'pulled out of the bag' in those dark days, so any light you can shed on the matter would be much appreciated.
All the best,
Kevin