Suppose the 2017 general election had gone very differently. Labour down to <200 seats, Tories triumphant.
Suppose that most Labour MPs were against Corbyn but couldn't remove him as leader (they've tried and failed already, of course).
Would the anti-Corbyn Labour bulk be able to nominate someone else to represent them in the House of Commons?
According to Wikipedia
The 1937 Act also contains an important provision to decide who is the Leader of the Opposition, if this is in doubt. Under section 10(3) "If any doubt arises as to which is or was at any material time the party in opposition to His Majesty's Government having the greatest numerical strength in the House of Commons, or as to who is or was at any material time the leader in that House of such a party the question shall be decided for the purposes of this Act by the Speaker of the House of Commons, and his decision, certified in writing under his hand, shall be final and conclusive".
Is there any guidance for how the speaker should make this decision (like there is for a tied bill in the Commons) or does he just do what he thinks best?
During WW2, Labour was allowed to hold the post of Leader of the Opposition, even though they were in Cabinet with the Tories, and the politicians who held the title Leader of the Opposition were not leaders of the Labour party.