David Cameron does not have an ideology, nor does he feel the need for one. The Prime Minister comes from a Tory tradition of elite prag­matists, instinctively suspicious of intellectual enthusiasm, regarding it as a gateway to immoderate dogmas. He recoils at the notion that there should be such a thing as Cameronism. He claims not to believe in "isms" of any kind.

That outlook has served him well, speaking as it does to a healthy British scepticism towards zealotry. It has made it hard for Labour to attack the government's austerity agenda as a wild-eyed crusade against public services. Early attempts by Ed Miliband to portray the Tory leader as a fanatical disciple of Margaret Thatcher failed partly because many voters still admire the Iron Lady and partly because the label doesn't stick.

Cameron has persuaded enough people that he is making cuts not because he wants to, but because he has to. The Labour leadership is now acutely aware that the public sees spending restraint as the hallmark of economic credibility. Ed Balls, the shadow chancellor, has committed a future Labour government to fiscal rules policed by the Office for Budget Responsibility – an innovation by George Osborne – and to making further cuts if necessary.

Miliband's hope is that, once it is established that Labour is serious about dealing with the deficit, the argument can be turned to the questions of how this is done and, crucially, as a member of Miliband's inner circle puts it: "Who pays?" The Labour leader believes that Cameron is vulnerable to the charge that he is making the wrong people foot the bill for the financial crisis – the young, families on low incomes, dinner ladies, nurses.

Threats by savages

The Tories want voters to ask themselves whether Labour knows how to govern without spending. Miliband wants them to ponder instead whose side Cameron is on. The Tory attack hinges on competence, the Labour one on values. So far, the Tories have been winning. Labour insists the public hasn't yet realised how badly Osborne's economic plans have failed and that, when it does, Cameron will struggle to mount a campaign based on a promise of more affable managerial pragmatism.

When it comes to turning the tide of opinion against Cameron, Miliband is greatly helped by Eurosceptic Tory backbenchers, whose mounting dismay at the Prime Minister's handling of the eurozone crisis is provoking dangerous questions about their leader's integrity.

Cameron professes to be a true Eurosceptic, held back from expressing his faith by two practical considerations. First, he must govern with the consent of Europhile Liberal Democrats. Second, an existential crisis in the eurozone is not the moment to present fellow EU leaders with a wish-list of powers for "repatriation". His position is to support efforts to save the euro while vigorously protecting UK interests in the wider single market. He has threatened to veto a treaty that does not meet that standard.

Yet Britain doesn't have the diplomatic clout to insert many provisos into a euro deal that will be designed by Germany and France. Bumptious backbench Europhobia is partly to blame for that weakness. Diplomats (and Lib Dems) complain that it is hard to make friends with fellow non-euro states – vital if single-market rules are not to be rewritten by a euro clique – when UK membership of the EU is openly regretted inside the Prime Minister's party. Ministers are forced to apologise for domestic Euro-bashing to their wounded Continental peers. As one Tory cabinet minister puts it: "Our national political culture can appear somewhat uncouth, even savage."

Britain has already been marginalised in Europe. The French and German model for rescuing the single currency envisages a new pact, hammered out in meetings of the 17 heads of eurozone member states, with wider economic reforms also on the agenda. Such a treaty might still include the ten non-euro states, but Cameron's promise to "safeguard" British interests will be hard to fulfil if he isn't in the room. That means any treaty encompassing all 27 EU members is bound to contain something that Tory backbenchers feel should be put to the country in a referendum – an outcome the government is determined to avoid. If Britain tries to veto such a deal, the 17 eurozone members can proceed without it.

In opposition, Cameron persuaded the Tories not to "bang on" about Europe because voters thought it an eccentric obsession unbefitting a reasonable party of government. The sceptics no longer feel bound by that deal, partly because Cameron failed to uphold his end of the bargain and win the general election, but mostly because they judge that Europe is no longer a fringe pursuit. They see it as central to the argument about how to revive the economy.

End of the beauty contest

The view on the right is that growth will be restored only with "supply-side" reform, cutting regulations and labour protections that are blamed for companies' reluctance to hire new staff. The ability to dump European employee rights is top of the Tory list of powers to be re­patriated. As one Eurosceptic MP puts it: "You can't have a supply-side revolution if everything has to be approved by the [EU] commissariat." Brussels bureaucrats are alleged to have strangled the economy in red tape.

Cameron might not possess an ideology, but many Tories do and hostility to Brussels is at its core. For them, the Prime Minister's bungled euro negotiations feel like treason. That isn't a view that Miliband shares, but it serves his strategy anyway. Cameron has thrived in an era when politics has been a beauty contest between leaders promising modified variations of the status quo. He needs to fight the next election offering steady-as-she-goes, pragmatic leadership, claiming that Labour has no realistic solutions to Britain's economic troubles.

Miliband's counter-attack will be that Cameron has made things worse and that he has no fixed values to guide the country in tempestuous times. He will say, in other words, that the Prime Minister is both incompetent and unprincipled. The Tory leader will be in trouble if his own party, feeling betrayed over Europe, starts saying the same thing.