UK 19 July 2019 Both Ed Davey and Jo Swinson could support a Labour prime minister And other lessons from tonight's Lib Dem leadership debate. Getty Sign UpGet the New Statesman's Morning Call email. Sign-up Both think they know how to win back Leave voters The first question put to both contenders was one that keeps some of their parliamentary colleagues awake at night: just how does the party of Bollocks to Brexit win support from the 52 per cent? Neither Swinson nor Davey showed any appetite to deviate from the full-throttle Remain platform that has paid such rich electoral dividends of late, but both acknowledged the party needed to develop an offer to Leave voters. But how? Interestingly, both couched their answer in terms of tackling climate change. Expect the winner to push for a British Green New Deal – a jobs-intensive policy that Lib Dem MPs believe would detoxify their Brexit message in post-industrial communities. The next Lib Dem manifesto will be as green as it is yellow Whoever wins will seek to burnish the Lib Dems' credentials not just as the leading party of Remain, but the best-placed party of the environment to win seats at Westminster. Both Swinson and Davey agreed that the government's net-zero carbon emissions target should be brought forward by at least a decade, and each had a list of domestic policy proposals as long as their arm on how to achieve it. That the environment and climate crisis has been so central to each of their leadership platforms guarantees that it will be as prominent a campaign theme going forward as Brexit, regardless of the victor Both Ed Davey and Jo Swinson say they could support a Labour prime minister – something their MPs believe is key to broadening their appeal. They won't really rule out putting Jeremy Corbyn into office Asked whether they would countenance a coalition or confidence and supply arrangement with a Corbyn-led Labour Party, the contenders answered in unison with a categorical no. Their granite face of unconditional opposition, however, crumbled under interrogation: Davey and Swinson in turn refused to rule out supporting a Labour government on a vote-by-vote basis. Significantly, Davey went as far as saying he would whip Lib Dem MPs to support a Labour Queen's Speech as long as it included legislation for a second referendum. As understandably wary as both candidates are of another coalition – they did, after all, lose their seats in 2015 – the price for securing their backing on a more informal basis is clear, as much as neither really want to admit it. On electoral pacts, both are keeping their powder dry Swinson and Davey both did a good job of creating the impression that they would be happy to agree to electoral pacts with Remain parties whatever the circumstances. Their shared refrain? "I'm not taking anything off the table." As with the Corbyn question, however, the devil was in the detail. Neither actually committed to anything. That, in part, is because the Lib Dem leader won't really have the power to: the party's hyper-democratic structure means that the decision ultimately lies with local branches. But there is another, altogether trickier issue at play too: the SNP and Plaid Cymru. Committing to stand down for the strongest Remain party in any given constituency risks conceding to both nationalist outfits in marginal seats formerly held by the Lib Dems (such as Ceredigion in Wales and North East Fife in Scotland), and would make Swinson's life as a Scottish MP very difficult indeed. The politics of a progressive alliance are much easier in theory than they are in practice – particularly when, unlike in Brecon and Radnorshire, the Lib Dems could lose out. This contest is about style, not substance Beyond its format, this evening's debate did not really seem like a debate at all. Such was the consensus between Swinson and Davey that it felt much more like a joint interview. As both candidates tacitly acknowledged in their opening statements, the question members must answer is who they think can communicate the same message more effectively. That there will be no real difference in what that message is was underlined by the fact that Swinson highlighted her media acumen above anything else. For now, at least, Cable or Huhne style internal dissent will be hard to come by. › The next prime minister must oppose UK involvement in torture Patrick Maguire was political correspondent at the New Statesman. Subscribe For daily analysis & more political coverage from Westminster and beyond subscribe for just £1 per month!