The "Letwin" amendment ...
- Any vote on the Brexit deal is not a legal approval until all necessary legislation for Brexit has passed.
Despite Letwin being a bit of an odd fellow ( he would vote for Brexit ) this is extremely clever, because if it is accepted it means the Benn Act is still in place ( Brexit Deal has not been approved ) and Johnson needs to ask for an extension this weekend.
It also closes the ERG loophole of voting for the deal today ( hence disabling the Benn Act ) and then next week torpedoing the Withdrawal Agreement to crash out with no deal.