UK MPs to vote on Theresa May's deal today
he PM said the changes meant the Irish backstop - the insurance policy designed to avoid a hard border in Ireland - could not "become permanent".
She insisted that she had delivered what Parliament asked her to do.
Tory Brexiteers and the DUP are taking legal advice on the changes but Labour said the PM had secured nothing new.
Two documents were agreed after Mrs May flew to the European Parliament on Monday with Brexit Secretary Steve Barclay for last-minute talks with Mr Juncker and EU chief Brexit negotiator Michel Barnier.
The first is a "joint legally binding instrument" on the withdrawal agreement which the UK could use to start a "formal dispute" against the EU if it tried to keep the UK tied into the backstop indefinitely.
The other is a joint statement about the UK and EU's future relationship which commits to replacing the backstop with an alternative by December 2020. ■