Government's Parliament Majority
A new referendum might actually be best. A lot of young people didn't vote because they thought it didn't matter. There's some evidence that the majority of the British population didn't want Brexit, but not enough to override an actual vote (I wouldn't see that as justified in the face of anything short of criminal tampering with the election, hard proof that the results cannot be trusted; here, no one's doubting that the votes of people who bothered to vote were counted accurately). "Let's vote again" seems the simplest and most direct way to deal with that. If the deal falls through, they would have sufficient impetus to call for one.