One of Jeremy Corbyn's biggest union backers has warned that he must form an "effective opposition" and make Labour look like a "government in waiting".

In an emergency motion to members, Unison declared lukewarm support for Mr Corbyn but issued a series of conditions he must meet and suggested that a leadership battle could be on the cards.

It follows reports that Mr Corbyn may not be automatically allowed on the official ballot paper if he faces a challenge because the party's rules governing such a battle are not clear.