The LibDems want a second referendum: on the terms of Brexit. Tim Farron has said that they will vote against triggering Aritcle 50 unless the government concedes a second referendum on the negotiated terms.
It is ironic that a party that opposed the first referendum now wants a second. In fact before they were against a referendum they were for one: In 2004 Chris Huhne said, “In a referendum campaign, the British public will be able to decide on the arguments themselves following an open debate. Without a referendum, the anti-Europeans would argue that the EU could only function by ignoring its peoples and Britain would be on the slippery slope to getting out altogether.”
Then, during the Lisbon Treaty debate, they flipped, opposing the referendum proposed by Conservatives on the grounds that what was required was an in-out plebiscite.
Now they want a second referendum on whatever terms the government negotiates. This looks awfully like the EU’s historic response to referenda that get in the way of further integration: Vote again until you get it right.
The idea of a second referendum is not, however, as stupid as the LibDems make it seem. Referenda are almost always binary, in this case Leave or Remain. While the Remain option was fairly clear (both the status quo and direction of travel of our relationship with the EU were known), Leave always encompassed a range of possibilities that have come to be typified (somewhat simplistically) as Hard or Soft Brexit. It is clear that those voting Leave had various and contradictory visions of Briain's future outside the bloc. A majority for a generic Brexit did not constitute a majority for any specific Brexit.
The idea of a referendum on final terms would at least have the merit of pitching relatively certain alternatives. There are, however, two serious obstacles that those proposing such a course must answer.
Firstly, it is by no means certain that, once invoked, Article 50 would be reversible. If not, we might be committed to leaving in spite of a second referendum failing to approve the agreed terms. Even if it were possible to withdraw from the Article 50 process, it would leave the UK in an invidious position. What sort of relationship would we have with other member states, with the EU institutions and with other countries with who we had suggested individual trade deals if, having negotiated for two years, we turned round and said we were not actually leaving?
Secondly, a referendum on the final terms would make negotiations all but impossible for the British government. The EU and member states would have every incentive to insist on the very worst deal for Britain (even at their own expense) on the assumption that the worse the deal, the less like a second referendum would be to approve it.
The LibDems may just be being opportunist in proposing a second referendum; those Conservative and Labour MPs and peers tempted to support them should now, however, get behind the government in negotiating the best possible deal for Britain to give effect to the stated will of the electorate.