Are there the numbers in the Commons to pass a Brexit deal?

Boris Johnson will likely have the support he needs if he keeps the DUP on his side – but the ex-Conservative MPs could throw a spanner in the works, writes John Rentoul

The prime minister will be hoping he is backed by the ERG MPs (PA)

Boris Johnson has built his Brexit negotiation on the two people who were furthest apart: Leo Varadkar, the Irish prime minister, and Arlene Foster, the leader of the Democratic Unionist Party.

Unexpectedly, in face-to-face talks in Merseyside last week, Johnson and Varadkar agreed “they could see a pathway to a possible deal”. In the negotiations that followed, Johnson kept Foster informed every step of the way.

That is because, while Varadkar is the key to an agreement with the EU, Foster is the key to securing a majority in the House of Commons for a deal. There are only 10 DUP MPs, but such is the balance of forces in this hung parliament that theirs are the critical swing votes.

The DUP still sustain the Conservatives in government – even though Johnson lost a formal majority when he expelled 21 MPs from the Tory party after they voted to legislate against a no-deal Brexit.

And the DUP enjoys a multiplier effect, in that several Eurosceptic Tory MPs who voted against Theresa May’s Brexit deal will follow its lead. Like the DUP, they are not just hostile to the EU, but they are passionate unionists. If the DUP accept that the Brexit deal preserves Northern Ireland as a part of the UK, then that is good enough for most of them.

So how might the numbers add up in the Commons? I think the easiest way to work it out is to start with the last vote on May’s deal, on 29 March, when she was defeated by a margin of 58 votes. That is, she needed 30 MPs to vote “Aye” instead of “No”.

Since then, the Tories have lost one seat to the Lib Dems in the Brecon and Radnorshire by-election, so Johnson needs to flip 31 votes. (Two Tory MPs have also defected to the Lib Dems since then – Phillip Lee and Sam Gyimah – but they voted against the deal anyway, because they want to cancel Brexit; they can’t be persuaded to vote for any deal.)

Johnson hopes to win over the 28 Eurosceptic Tories who refused to vote for May’s deal, and who revel in the nickname “the Spartans”, in ignorance of what happened in the battle of Thermopylae, a heroic defeat.

He has appointed four of them to jobs, including Priti Patel and Theresa Villiers, and Steve Baker, chair of the European Research Group, was consulted on the prime minister’s proposals and supported them.

Some of the Spartans, such as Owen Paterson, are said to be unhappy that Johnson has conceded too much, so it is possible that a handful of them will hold out, but my guess is that, if the DUP remain in favour, about 25 of the 28 will vote for the deal.

That would give Johnson the votes he needs: 25 Tories plus 10 DUP.

It is possible, however, that some of the 20 ex-Tory MPs currently sitting as independents who voted for May’s deal might switch from “Aye” to “No”. Amber Rudd, for example, who gave up the Tory whip voluntarily, said she thought Johnson’s deal would “hit manufacturing”. David Gauke, the former justice secretary who ran Rory Stewart’s leadership campaign, was worried it might incur an “unnecessarily high economic cost”. But others in this group look forward to returning to the Tory fold if they vote with the government.

What is more, Tory switchers against the deal might be offset by MPs of other parties switching in the opposite direction. Stephen Kinnock, the Labour MP, leads a group called “MPs for a Deal”, which has 12 Labour members who didn’t vote for May’s deal but say they could vote for a new deal if it respects workers’ rights – plus one Lib Dem, Norman Lamb, who is standing down at the next election.

I doubt if many of the 12 Labour MPs will vote for the deal, especially as Jeremy Corbyn has shown an uncharacteristic disciplinarian streak and threatened to expel them if they do so, which would prevent their standing as Labour candidates next time. But Kate Hoey and Graham Stringer, Labour’s own Spartans, will probably also vote for a deal if the DUP does.

So Johnson could have the votes in the Commons for a deal, as long as he has the DUP on his side. But his fate could be decided by ex-Tory and Labour “soft Brexiters” including Rudd, Gauke and Kinnock.