It is one that takes no account of party political lines or internal party divisions.

To those who take a view on it, joining or staying out of EMU carries such crucial constitutional implications that an individual politician's position on it transcends mere party loyalties.

This has led to some unlikely political interventions.

The Times supports ... lefties

Take for instance The Times newspaper, owned by that arch-Eurosceptic Rupert Murdoch - the Australian-born American-turned media baron who is said to cause grown cabinet ministers to think more than twice before proposing policies contrary to his views.

The two Kens in favour: Labour left-winger Livingstone . . .

The Times is the upmarket flagship of Mr Murdoch's UK press interests. Like its proprietor, it was a loyal and loving supporter of Margaret Thatcher during her reign as prime minister.

But at last year's general election it adopted a "principle not party" stance, with Europe and EMU the defining issue. And so it backed Eurosceptics of left, right and centre.

On polling day the paper printed a guide to the most anti-European candidate in every constituency.

Voters enjoyed the bizarre spectacle of a Murdoch-owned paper instructing its readers to support stalwarts of the Labour left like Diane Abbott and Jeremy Corbyn, as well as Conservatives such as Bill Cash and John Redwood.

. . . and Tory ex-chancellor Clarke

To see Ms Abbott and Mr Corbyn, both members of Labour's Campaign Group of MPs, as representing the left-wing view of Europe and EMU would be a mistake, however - for the simple reason that there is no monolithic left-wing, or for that matter right-wing, view of Europe.

The euro fans

Their fellow Campaign Group member, Ken Livingstone MP, is pro-European and EMU-friendly. With him in the pro-euro corner is that other famous Ken, the Tory ex-Chancellor, Mr Clarke.

Equally euro-enthusiastic is the left-wing Labour MP Brian Sedgemore.

Come the referendum on joining the single currency, UK euro fans can expect to see in their ranks former deputy prime minister Michael Heseltine, ex-premier Edward Heath (both Tories), Liberal Democrat leader Paddy Ashdown, Euro-federalist lefties such as Hugh Kerr and Ken Coates (the MEPs expelled from Labour and now standing as independents), modernisers like Euro-commissioner and ex-Labour leader Neil Kinnock, Trade Secretary Peter Mandelson, the leadership of business associations like the Confederation of British Industry, and the Trades Union Congress.

Strange alliance against: Jeremy Corbyn MP . . .

It is an eclectic grouping which under normal circumstances you would not expect to gather in the same room without a fight breaking out.

Fighting the euro

Not that the anti-EMU alliance is any less startling.

Baroness Thatcher, left-wing Labour MPs Alan Simpson and Dennis Skinner (both in the Campaign Group), Tories Michael Portillo and Teresa Gorman, Conservative leader William Hague, former Labour cabinet ministers Lord Shore and Lady Castle, the Institute of Directors - and association of big business chief executives - and some left-wing trade unions like the Transport and General Workers' Union are likely to fight on the same side.

They will receive much useful support not only from Mr Murdoch's publications, but also from those of Conrad Black, the deeply Eurosceptic Canadian owner of the Telegraph newspapers.

. . . and media baron Rupert Murdoch

The anti-single currency cause has a history of attracting successful businessmen who believe they have a good cause to fight and lots of money to spend on it.

The late Sir James Goldsmith founded and bankrolled the anti-EU Referendum Party which put up candidates at the last general election.

The remnants of his organisation have been taken over and given new financial muscle by Paul Sykes, the former Barnsley tyre-fitter now worth an estimated £250m.

He quit the Tory Party two years ago in protest at John Major's refusal to rule out a single currency, and doled out £2m to Eurosceptic Tory candidates at the general election.

Since then he has pledged to spend £20m on a lavish "Britain Says No" campaign.

It looks set to be the only substantial opposition to a government-backed Yes-campaign when the EMU referendum is called.

The outcome of such a referendum is no sure thing - which helps explain why the government is so jittery about when to hold it.

Whatever the eventual result, it would be remarkable if the single-issue, strange-hued rainbow coalitions that will come together on either side of the argument do not immediately fall apart very shortly after the polling booths shut.