He has sent a letter to Theresa May offering Labour support for a deal in Parliament if it includes five legally binding elements:
* A “permanent and comprehensive UK-wide customs union”, including a say in future trade deals.
* Close alignment with the single market, underpinned by “shared institutions”.
* “Dynamic alignment on rights and protections”, so that UK standards do not fall behind those of the EU.
* Clear commitments on future UK participation in EU agencies and funding programmes.
* Unambiguous agreements on future security arrangements, such as use of the European arrest warrant.
This could open the door to an alliance in the Commons between moderate PM-supporting 'soft Brexit' Tories and the bulk of Labour MPs, which would get the deal through.
It's a major shift for Labour and opens up new possibilities. The list is do-able for May and much of it she supports anyway.
This might be the death-knell for Rees-Mogg and the hardline fantasy-Brexit mongers, but it's difficult to tell if May will go for it, since accepting it will make the division in the Tory Party permanent and unsolvable - even to divide.
Quite a big development and perhaps too late in the day now - unless May goes for it and then calls a general election, which seems a possibility.
We live in interesting times.