Reading comments made by Tom Watson and Jeremy Corbyn plus John McDonnell it occured to me that they don't seem to be talking to each other much. I thought that as Deputy Leader Tom and Jeremy would be doing a lot of chatting .
Not really answering your question, but it's just struck me as mildly amusing that I read Tom and Jeremy as Tom and Jerry. Probably do just as good a job.
A cynical political move to support a chance to overthrow a democratically arrived at decision in the hope that they can add remainers to their core labour voters. Can't see how they could resist slinging morals away in favour of such a power grab. All the more reason to get Brexit done and dusted, probably by no-deal, before any GE.