Campaigning for the Conservatives in Cheshire last week, David Cameron dodged questions about British prime minister Theresa May’s bonfire of his policies on everything from grammar schools to pensioners. Regardless of their differences, he is hoping the prime minister will win next month’s election by a landslide.

“This is one of the most defining elections I can remember where it’s so important that the Conservatives win and win well, so Theresa can negotiate that Brexit deal and stand up to people who want an extreme Brexit, either here or in Brussels, ” he said.

Some even hope that, having defied the headbangers on the right of her party, she might even contrive to keep Britain inside the single market

Cameron’s view is shared by optimists in Britain and elsewhere, who believe that a comfortable majority will allow May to soften her approach to Brexit and make the necessary compromises to secure a mutually beneficial deal with the European Union. Some even hope that, having defied the “headbangers” on the right of her party, she might even contrive to keep Britain inside the single market and the customs union.

Manifesto

The campaign itself has made such an outcome more remote, however, and this week’s Conservative manifesto maps out a hard Brexit, explicitly promising that Britain will leave both the single market and the customs union. Until now, May kept the door to the customs union slightly ajar. The manifesto slammed it shut.

"David Cameron’s view is shared by optimists in Britain and elsewhere, who believe that a comfortable majority will allow Theresa May to soften her approach to Brexit and make the necessary compromises to secure a mutually beneficial deal with the European Union." File photograph: Neil Hall/Reuters/Files

The commitment is important because parliamentary convention prevents the House of Lords from voting down any measures promised in a governing party’s manifesto. The manifesto also commits May to reducing annual net immigration to the tens of thousands, prompting German chancellor Angela Merkel to warn that the EU could retaliate against too strict a policy.

A highly centralised candidate-selection process has ensured that few of the new Conservative candidates are known zealots on Brexit

May could, of course, break her manifesto promises. But in a campaign which has been all about her leadership, she has sold herself as a straight talker who is true to her word and follows through regardless.

“At last, a PM not afraid to be honest with you,” said the front-page headline in Friday’s Daily Mail.

Her electoral strategy is based on absorbing the Ukip vote into the Conservatives and capturing Labour-held seats in places which voted Leave in last year’s referendum. A highly centralised candidate-selection process has ensured that few of the new Conservative candidates are known zealots on Brexit. But most the new intake of MPs will owe their success, at least in part, to their voters’ determination to see Brexit through.

One clear advantage of May’s decision to call an early election is that she will have five years before she has to face the voters again. This would give her three years after the end of article 50 negotiations in March 2019 to negotiate a free-trade deal with the EU, during which time transitional arrangements could apply.

"The leaked account of European Commission president Jean-Claude Juncker’s dinner at Downing Street last month exposed how far apart Britain and the EU are in their approach to the negotiations." File photograph: Jean Francois Badias/AP

But there is a growing sense, in London as well as Brussels, that negotiations may not reach that point and could collapse before the end of this year. The leaked account of European Commission president Jean-Claude Juncker’s dinner at Downing Street last month exposed how far apart Britain and the EU are in their approach to the negotiations.

Financial settlement

The EU member states have agreed detailed negotiating guidelines, which rule out starting talks about Britain’s future relationship with the EU before progress is made on other issues, such as citizens’ rights and the divorce bill. The EU’s line on the financial settlement has toughened in recent months, mostly at the urging of the member states rather than the commission.

The British know that the money is one of the few pieces of leverage they have in the negotiations

Net contributors such as Germany and the Netherlands are unwilling to make up the shortfall in the budget caused by Britain’s departure, and net beneficiaries do not want to see their payments cut. This creates a powerful incentive for the EU to press for the biggest possible financial settlement from Britain and to agree the outline of that deal before the end of this year.

The British know that the money is one of the few pieces of leverage they have in the negotiations, so they want the financial settlement to be part of the broader negotiation about Britain’s future relationship with the EU. The fear in Whitehall is that the EU’s approach to the negotiations will be as inflexible as it has been in accession talks with new member states or bailout negotiations with Greece and Ireland.

If initial talks about the negotiating timetable and the financial settlement go badly, May would have to consider if further negotiations are the best use of Britain’s time before it leaves the EU in 2019. One option is to walk away from the talks later this year, telling the EU that Britain will prepare to leave with no deal, but is open to talking about arrangements to make its departure less disruptive for both sides.

Such a step would be bad for Britain, for Europe and for Ireland, but if she takes it, May will be greeted with cheers and fluttering order papers by her Commons majority and roars of praise in the Daily Mail.