Hmm, it's quite a mystery. Reason I asked is because I was writing a basic account of the M.52 story for my forthcoming Lightning book and although it's easy to re-trace the story as related in many books and magazines, there's hardly any evidence to support what is repeatedly said.
As far as I can determine, there doesn't seem to be any obvious single cause for the cancellation and it was probably due to a variety of factors including cost (the Government was nearly bankrupt), risk (there wasn't complete confidence in the design, although it seems odd that it was allowed to progress so far), American pressure (it seems clear that they wanted all the credit for their X-1 project) and Barnes Wallis trying to secure rocket model work for Vickers.
I just don't know how the un-supported story has persisted for years that the M.52 data was handed-over to Bell in exchange for American "data" (about what?) which never materialised. The story seems plausible but there doesn't seem to be any evidence to support it. I don't imagine that the M.52 data was handed-over for nothing, and yet there seems to be no evidence of what we were expecting (or actually received) in return. You'd think that after all these years there would be, and yet all one finds is endless repetitions of the same basic story, without any factual information to support it.
It's quite a saga!