Interesting thing about this bit of textual sophistry: it fails on its own terms, because it misrepresents Norgrove's letter.
Norgrove didn't say what Johnson says he said. He objected to Boris mentioning 350m "in connection with the amount that might be available".
Norgrove didn't, in fact, claim Johnson said £350m would be available to spend. He was objecting to the figure being used at all.