Heidi Allen boosts the Lib Dems – but they risk winning ‘wasted votes’ without a thaw in relations with Labour

After Boris Johnson resigned from Theresa May’s cabinet in protest at her proposed Brexit deal, his allies told me confidently that when he succeeded her as prime minister, we would see “a very different Boris”. They added: “From day one, he will revert to the One Nation Conservative who was London mayor.”

The reality has been the opposite. Brexit has driven Johnson down a very different track. The threat from Nigel Farage’s Brexit Party, and a looming general election, has persuaded him to vacate the centre-ground and lurch to the Eurosceptic right. The latest aggressive briefings from Downing Street suggest the Tories might fight the election as a no-deal party – a huge gamble, since four million Conservative supporters backed Remain in the 2016 referendum.

Johnson is chasing the votes of Labour Leavers in the north and midlands, possibly at the risk of losing Tory heartlands in the Home Counties and London suburbs. At last week’s Tory conference, I was struck by the gloom among moderates. As one told me: “The die is cast now. We are powerless to stop it.”

These developments are very good news for the Liberal Democrats.

With Jeremy Corbyn’s Labour playing on the left wing, the gap in midfield is unusually large. Normally, our two biggest parties claim to pitch their tent on the centre ground. Today, there is little pretence.

So the Lib Dems have the big opportunity they've been awaiting for nearly half a decade. Six months ago, they had 11 MPs and were still in the post-coalition doldrums. They have since toasted big gains in local and European Parliament elections. Their new leader Jo Swinson could hardly have taken over in more favourable circumstances in July. She has made a confident start, and the momentum has continued on her watch.

Her party now has 19 MPs, after the former Tory and Change UK MP Heidi Allen told The Independent last night she's joining it after months of rumours.

For all that Johnson claims to be a liberal conservative, he seems to have unwittingly become a recruiting sergeant for the Lib Dems. Removing the whip from 21 Tory MPs who opposed a no-deal Brexit was an open invitation for them to cross the floor; Sam Gyimah, one of the Tories’ brightest young stars, was the first to do so.

Allen told us that at least 20 One Nation Tories would like to join her in the Lib Dems. This morning on Radio 4’s Today, she gave a more realistic estimate of actual defections, saying: “I imagine it must be going through the minds of at least half a dozen of them.”

Walking out on your political family is hard to do. Making the leap to a party you have fought hard against for years is even harder. Some former Tories will fight their seats as independents rather than join the Lib Dems, like Dominic Grieve, the former attorney general, whom the Lib Dems have now said they’ll not stand against when the election comes. Rory Stewart, another of the 21 outcasts, said he did not want to campaign as an independent against former Tory party members in his Cumbria constituency; he will run for London mayor, again as an independent.

The Lib Dems will be hoping for some last-minute defections when the election is called. Every new recruit will help them counter the “wasted vote” argument that has long haunted them at general elections. The squeeze will take a different form this time.

The Tories and Labour will both claim voting Lib Dem will help the other main party. Crucially, Boris is banking on a split in the Remain vote between Labour, the Lib Dems and Greens. If the Lib Dems do only fairly well, the Tories could win some Con-Lab marginals with a lower share of the vote than they got in 2017. But if the Lib Dems manage to produce a genuine surge, they could scoop up enough Tory seats to offset the governing party’s gains.

Swinson, naturally, is aiming high. But it won’t be easy to translate her party’s momentum into scores of seats under our archaic first-past-the-post system.

Allen delayed her defection, which I predicted in July, to work on Unite to Remain, a campaign she hopes will see a single Remain candidate from the Lib Dems, Greens, Plaid Cymru and independents such as Grieve in more than 70 seats in England and Wales. Such electoral pacts could harm Johnson’s chances of winning a majority on the back of a divided Remain vote.

But it will take more than that to defeat him. Labour is the big missing piece of the Unite to Remain jigsaw, and its relations with the Lib Dems are frosty at best. So in the majority of winnable seats, Remainers and supporters of a Final Say referendum will need to vote tactically to bridge the gap themselves.