T&N - I am not going to engage in this silly style of typing up a series of outbursts and adding the suffix "inconvenient truth!" after each one. That is knockabout kindergarten stuff. Besides, that phrase is closely associated with a former US presidential candidate whose own wild claims under that title have been widely discredited. However, I will address factual points raised.
Firstly, you are presuming that the research published by Spatial Economics Research (your source) is superior to that of the Sheffield Political Economy Research Institute (my source). It may indeed be so, but I don't know this and neither do you. It is a moot point. But neither source can be discarded because the other suits our case better.
Now, addressing some of the numbers which you quote from Spatial Economics. Firstly, that GBP400 UK Average figure which you quote (it is actually the English average BTW) includes London. This of course has the effect of making that GBP400 number far higher than it would otherwise be. Next, the GBP770 figure which you quote relates to projects where the public sector is sole funder. It is therefore appropriate to use the higher GBP2500 number which includes projects which are partially funded by the public sector. And based upon those numbers - from the research which you cite - my 'multiples' claim is validated. As for your noting that I have downgraded my original multiple, this is a nod to the maths provided by Spatial Research. Neither of us can say that Sheffield P.E.R.I.'s numbers were the invalid ones.
Next, M4/M25 measures. What upgrades may or may not be required there in the future is pure speculation. What will or will not be funded is unknown. I see no 'inconvenient truth' established there. I see conjecture.
On spending GBP5Bn-20Bn in the NE. Firstly, let's be quite clear. I have never proposed anything of the sort. As for what the multipliers and benefits of an undefined future notional project might be, nobody knows. Claims to the contrary make no sense. By the way, I propose fairer distribution of public infrastructure expenditure around the regions generally, targeted at projects of high merit. I have never suggested a single 'big-hit' one-off project. And whilst I support a fair deal for the NE (amongst others) note that it is not my own region. As for your contention that spending in the SE will in all cases provide better ROI than spending in the regions: utter hogwash. Although I can certainly appreciate the advantage to SE interests of promoting this myth!
There is , as you say, significantly higher private investment in the SE than in the regions. However, much of this goes on projects to which the public sector contributes. There is a need for this investment model to be encouraged regionally.
Finally, it seems that you have conducted a nationwide plebiscite on support for LHR R3. Amazing. Care to share your full results with us?