Polling and Brexit policy are certain to be high on the agenda this weekend as Labour activists gather in Brighton for their annual conference. A volatile political year has transformed the political landscape since the last annual gathering. The polls were upended this spring in the wake of Theresa May's failure to secure a Brexit deal and departure from Downing Street, with surges in support for two parties representing opposite extremes of the Brexit debate - Nigel Farage's newly founded Brexit party and the strongly pro-EU Liberal Democrats. Support for the Brexit party has faded since (they score 12% in this week's Opinium poll), but the Lib Dems have held on to their gains and are now nipping at the heels of Labour - the poll gives 17% to the Lib Dems and 22% to Labour (who are 15 points behind the Conservatives on 37%).

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The Lib Dem recovery has been driven by Remain supporters, among whom they are now tied with Labour (each gets 33% of the Remain vote in the poll). This raises questions about the sustainability of Labour's perpetually ambiguous stance on Brexit, which underwent yet another round of cautious evolution this week. Labour now says it will fight an election committed to a second referendum, with Remain as one option and a "credible Leave option" as the other. That is a long way from its 2017 manifesto position, which committed Labour to honouring the result of the first referendum. But this shift may not be enough for tribal Remain voters, who now see the Lib Dems as a more credible champion of their cause, particularly as Labour refuses to commit in advance to campaigning for Remain in a second referendum. The risk for Labour is that seeking the middle of the road on Brexit gets them run over by an electorate no longer interested in compromise - 69% of voters rate Labour's current Brexit policy as "unclear" and 63% disapprove of Corbyn's handling of the issue.

How worried should Labour be? The electoral risks are mounting. Labour has lost half of its 2017 support, and some polls now put them behind the Lib Dems overall. Jeremy Corbyn's personal ratings have slumped since the 2017 election and are now the worst ever recorded for an opposition leader. Labour optimists will point to the party's dramatic turnaround in the previous general election campaign as evidence that there is no need to panic. Once an election is upon us, Remain voters will again recognise that Labour is the only viable alternative to a hard Brexit Conservative government, and will return to the fold. The Lib Dems' rise may even play out in Labour's favour, if the Lib Dems challenge the Conservatives in southern English seats where Labour is out of contention, while being tactically squeezed in Conservative-Labour marginals where Labour is best placed to defeat the Conservatives.

• Robert Ford is professor of Political Science at the University of Manchester and co-editor of Sex, Lies and Politics