It's not cobras, TTT, although the irony is that (I think) you're missing the entire point of that claim. It *is* false, and it's stupid to pretend otherwise, that we sent the EU £350 million a week. As I pointed out above, official statistics show that it is never true and has never been true. Cummings replied to the letter and argued otherwise, but even that I think played into his objective. You've got to back up a claim you know to be false if there's a purpose behind the false claim.
As far as I can see in retrospect, the point is that Voters would see/hear (apologies for caps, but it's important to make the point visually):
WE SEND THE EU ᵗʰʳᵉᵉ HUNDRED ᵃⁿᵈ ᶠᶦᶠᵗʸ MILLION POUNDS A WEEK
which sounds like (and is) a lot. Remain voters and campaigners saw the "350", looked into it, realised it was wrong, and kicked up a fuss. But, of course, their correct calculations turn the figure into 250, or possibly 175 million a week. In other words:
1. Everything in the original claim in capitals remains true;
2. All of the arguments against the claim merely serve to reinforce its main point;
3. Therefore, why should we as voters care about the precise figure? We send the EU a large amount of money each week, and it sounds like way too much.
The £350 million a week lie was, possibly, genius, if seen from this perspective. It's wrong, but it was right in all the ways that mattered.