Nick Clegg has warned his coalition partner David Cameron against reversing centuries of British engagement and leadership in Europe, declaring that discussion of a referendum on relations with the EU before the euro has been rescued would place "the cart before the horse".
In a Guardian interview before the 40th anniversary of British accession to the European Economic Community on 1 January and a landmark speech by Cameron on Europe, Clegg pleads for Britain not to sell itself short and to recognise the influence it can still exercise on Europe's direction.
He insists he is "not frightened" of a referendum, but adds: "For the life of me I still don't know what is the question we're supposed to be putting to the British people because we don't yet know what we're reacting to in terms of the further integration of the eurozone."
Clegg's interview launches a three-day Guardian series which looks at the state of Britain in the EU. The Guardian has interviewed leading players, past and present, in Britain and on the continent.
In a sign of the backbench pressure facing Cameron, the leading Tory Eurosceptic Andrea Leadsom has revealed the Fresh Start group of Tory MPs will next month publish their proposals for a Conservative renegotiation of the terms of Britain's EU membership.
This will include two "nuclear" options on financial services and the working time directive.
The former banker tells the Guardian: "If there is a treaty change what we have to be doing long in advance is saying to our European colleagues: 'Here is one we prepared earlier. There is a trade here. You want to completely change the terms of the EU. You want to go to fiscal union – that was never the deal so here is what we want in return.' It needs to be a completely full, rounded renegotiation."
The 40th anniversary series shows that political pressure is building across the spectrum. The pro-European former Labour cabinet minister Shaun Woodward argues that a referendum may be the only way to save Britain's EU membership.
The challenge to pro-Europeans is highlighted in the latest Guardian/ICM poll, which shows that a majority of voters are opposed to British membership of the EU. A majority of 51% indicate they would vote to leave, while 40% say they would vote to stay in.
The last time ICM asked the same question, in autumn 2011, the figures were 49%-40%, while in 2001 there was overwhelming support – 68% – for membership.
Clegg insists Britain should focus on helping to fight the crisis in the eurozone rather than attempting to renegotiate the terms of its membership. The prime minister is widely expected to use his long-awaited speech in the new year to announce that if the Lisbon treaty is rewritten in a substantial way to underpin the euro after the 2015 general election he would demand the repatriation of some powers as the price of British support. The Conservative manifesto for the 2015 general election would then contain a pledge to hold a referendum on the new package.
Clegg is dismissive of the prime minister's approach. "What we really should be doing is just focusing on the kind of economic firestorm at hand, working co-operatively to help them to put out the fire in the eurozone and to come out of this phase of economic emergency. I think to have a referendum, kind of about nothing very much in particular, when you're in the middle of an emergency repair job to your own economy and European economy, is putting the cart before the horse.
"It's an exercise of political shadow boxing to try and anticipate a process of which we're not one of the principal authors and then start now prescribing how we should react to it."
Clegg warns that such a strategy would abandon decades of successful British engagement in Europe. This saw prime ministers from Margaret Thatcher to Tony Blair "exercise extraordinary leadership" in the EU's two great historic triumphs – the formation of the single market and the enlargement to the east.
"At every point when there's been a fork in the road about whether Britain should retreat or lead, when we have led we have always surprised ourselves and others about how successfully we can lead.
"It would be a dramatic reversal of not just decades but centuries of British engagement and leadership if we were to suddenly back ourselves out of the whole enterprise, but it would also in my view have a very detrimental effect on the balance of opinion, the balance of debate in the rest of Europe.
"It short changes us as a country to assume always that we cannot lead when all the evidence is, throughout our history, even if we're not in the centre of the action that's going on across the Channel, that we nonetheless can bring great leadership to bear."
Clegg also challenges the Tories in two sensitive areas on Europe as he warns his coalition partners that:
• A review of the "balance of the EU's existing competences", which is being carried out across Whitehall as part of the coalition agreement, could end up making the case for greater British involvement in the EU. "They [the Tories] might be quite surprised that the more you actually look into it in detail, a lot of it you think is not a bad thing at all sometimes."
• Plans to try to distance Britain from many EU law and order measures may harm the fight against crime. The coalition will exercise Britain's right to opt out of around 130 EU measures. Clegg is keen to opt back in to many of these, such as the European arrest warrant, while Cameron is more wary. Clegg says: "I just don't think it would be explicable to anybody why we would do anything to diminish our protection against crime."
The deputy prime minister insists the Liberal Democrats support reform of the EU, saying: "It needs to be more competitive, more lean, more transparent, more democratic and less wasteful in places, but you achieve those aims by getting stuck in.
"You can get reform by exercising leadership rather than withdrawal. To win you need to be in it."
But in the face of strengthening Eurosceptic opinion in the UK he unashamedly makes the case for the European Union, describing its strength in numbers as "the most compelling answer to the insecurities of globalisation".
He says: "I think the extraordinary resilience of European integration lies in the fact that, whilst its origins may lie in our blood-drenched European history – Franco-German reconciliation after the war – its future actually lies in addressing a wholly different and modern challenge which is the challenge of globalisation."
But he warns: "I don't think anyone should be under any illusions. Globalisation isn't going to go away. Once we're through this period of intense turbulence, this mid-life crisis as far as the eurozone is concerned, we in Britain will still be faced with a globalised world."
He admits that story cannot be told clearly now because of the internal imbalances in the eurozone.
He also claims the eurozone is inching bit by bit to putting together "a new north/south deal between creditor and debtor countries, where northern creditor countries have to admit to their own taxpayers that they are on the hook to help the weaker economies of the south and the governments in southern Europe need to admit to their voters that they will be subject to a level of discipline and scrutiny in their economic policy from Brussels and from Berlin which is much more stringent than it was before. That's the deal.
"Everyone wants it done by next Tuesday. It won't, but it will slowly take shape and everybody knows that is where they are going".