WITH JUST a month to go before Britain is due to leave the European Union, both the country’s main parties have shifted their positions on Brexit. Theresa May, whose maxim as prime minister has been that “no deal is better than a bad deal”, has offered Parliament a chance to forestall such an outcome. Meanwhile Jeremy Corbyn, who has long resisted the calls of Labour Party members to back a second referendum, has said that in some circumstances Labour would support one.

In a statement to Parliament on February 26th Mrs May said that MPs would get another chance to vote on her draft exit deal by March 12th. If they reject it, as they did last month by a large margin, she said that she would put forward a motion by March 13th to leave with no deal. If that motion is rejected—as straw polls of MPs suggest it would be—the government would on March 14th put forward a motion to request a “short, limited extension” to the Article 50 Brexit negotiations. Mrs May said that such an extension would run “not beyond the end of June”, to avoid dragging Britain into this spring’s elections to the European Parliament. Her plans therefore do not rule out a no-deal exit, but rather give MPs the chance to postpone it for three months.

Labour, meanwhile, says that if Parliament rejects its own rival plan for Brexit, then it will back an amendment demanding what it calls a “public vote”, which would include the option to remain. But check the small print: Labour is proposing that such a referendum take place only after Parliament approves Mrs May’s deal, as what Mr Corbyn calls a “confirmatory” measure. This renders the plan fairly pointless, as one of the main arguments for a second referendum is that it would be a way to break the current parliamentary deadlock. If MPs did manage to agree on Mrs May’s deal there would be little appetite for a second referendum.

Both parties’ measures are therefore less radical than they might appear. Mrs May made her move only in order to head off a rebellion by ministers who are opposed to leaving without a deal. And Mr Corbyn seems to have softened on the question of a second referendum mainly to keep his own supporters and MPs on board (nine quit the party last week for various reasons, including his position on Brexit).

Yet although the concessions are small, they have opened the door to bigger ones. Mrs May has repeatedly said that Britain will leave the EU on March 29th, deal or no deal. Her position now is that Britain need not leave on that date, and that MPs must have a say on whether leaving with no deal is acceptable. Now that the principle of delaying Brexit has been conceded, the arguments can begin about the length of the delay. Likewise, Mr Corbyn’s acknowledgment that voters should have a say on the final deal opens the door to debates about the conditions under which such a referendum should take place.

This week’s shifts may be small in practical terms. But they are significant concessions of principle. They could, in the tumultuous month ahead, lead both parties to change their positions yet again.