We are at a defining moment, not only for the next two or three years of Britain’s relations with the European Union, but also for Prime Minister David Cameron’s relations with his Conservative party. Cameron is carrying both to the point of crisis over the appointment of Jean-Claude Juncker as president of the European Commission. If he overcomes Juncker’s majority-support in both the European Council and the European Parliament and succeeds in placing a “reformist” alternative at the head of the Commission, he will be able to keep a lid on the anti-EU passions simmering in the Conservative party. The price will be a further loss of influence in Brussels and the prospect of EU reforms that will fall very much short of the ambitions of his party at Westminster and its restless grassroots support.

Only the imminence of the general election next May will avoid truly destructive unrest in the Conservative party and save Cameron’s leadership if he loses the battle of Juncker. Pressure from his party to seek daily rows with Brussels will be stepped up in the hope of keeping Nigel Farage’s UKIP at bay. Be prepared for allegations of unacceptable steps towards federalism in every Commission proposal. The UK’s approach to Brussels will be reset from “difficult” to “hostile”. There will be more demands from the grass roots for an in-out referendum even before the election. There is a hunger for more fundamental reforms in the terms of British membership than Cameron can possibly deliver from any negotiation. His “we are being forced towards the exit card” has already been played to the resentment of Chancellor Merkel and the German parliament and will be a busted flush if Juncker is appointed.

With or without Juncker in the Berlaymont, Cameron knows that the reform process cannot be completed by next May. But he will need to persuade the Commission and the Council to go beyond general statements of reform priorities to avoid backbenchers resurrecting Margaret Thatcher’s famous contempt for “fudges” in Europe and demanding that he ask for much more.

Cameron’s campaign is making only modest progress. There are other leaders in the European Council who share his reluctance to cede control over the Commission appointment to the parliament. They may be unhappy with the process but they are also much more sensitive than the British prime minister to the view that the Spitzenkandidaten experience is a deepening of democracy in the Union. As yet, there is no clear blocking minority rallying to the British flag in the European Council. Next week’s summit looks likely to try to buy time by agreeing to identify priorities for EU reform before confirming Juncker or an alternative at the head of the Commission.

It is not at all certain that Cameron has any clear red lines when it comes to “getting tough” with Europe. There are those who hold that he wants Britain to stay in the EU and will campaign for a yes vote if he manages to call a referendum in 2017. Others believe that he is a politician of few convictions and will do what he has to do to hang on to power – even committing to supporting Brexit. In the meantime, shadows over his authority on European matters are lengthening. Having made the strategic error of encouraging European Parliament Conservatives to withdraw from the European People’s Party in 2009, his MEPs are now out of control. They cared little about upsetting Chancellor Merkel last week by ignoring Cameron’s appeal to keep seven members of Germany’s anti-euro AfD party out of the European Conservative and Reformist group.

The one factor that could carry Cameron past the Scylla of reform negotiations and the Charybdis of the Conservative clamour for Brexit are the strengthening hopes in the party of a Conservative victory in the general election. This would massively bolster his authority at home and yield added leverage in Brussels, and is by no means as fanciful as it seemed only a few months ago. The UK is currently enjoying a stunning economic turnaround that has yet to make an impression on living standards but is the fastest rate of annual growth among the developed economies. There may yet be a feel-good factor in time to put wind into the Conservative sails. The Labour Party’s lead in the polls is far too small to be impregnable while the Liberal vote looks likely to collapse. Much depends on whether UKIP could make enough gains to hold the balance of power at Westminster after next May.

The best advice to be given to those in the wider world from Berlin to Washington and Paris to Peking who worry about a potential political upheaval in the EU is to bear in mind that neither Conservative Eurosceptics nor UKIP appear yet to be leading public opinion on Britain in Europe. On the contrary. Hostility to EU membership is now outweighed in the polls by pragmatic support for staying in a vaguely reformed but less intrusive EU. The weight of recent critical analysis of the illusory benefits of British withdrawal combined with warnings from business about potential economic harm are beginning to have an impact. Cameron will still have to fight on two fronts; his political future and Britain’s national interests require him to win on both.