Trident provokes passionate debate - but it should be seen as a practical issue rather than one of ideology

As Jim Murphy, Labour’s leader in Scotland, remarked during the last television debate, much of the coverage of the election is about the horse trading that will begin on 8 May rather than about the issues that will be at stake 24 hours earlier on polling day. Nowhere is this clearer than on defence. Defence is vital, yet the arguments have been too readily reduced to what the Scottish National Party (SNP) might or might not do in the House of Commons with MPs who are, as yet, not even elected.

The debate was debased further when the Defence Secretary, Michael Fallon, hitherto one of David Cameron’s quiet cabinet successes, used Trident to launch a silly and futile personal attack on Ed Miliband. At his age – he has been kicking around the political scene since he served as a junior minister to Margaret Thatcher – Mr Fallon really ought to know better. As has been noted, if Ed Miliband is tough enough to betray – “outsmart” is a better term – his brother, he is tough enough to face down Nicola Sturgeon. One wonders if the Tories are getting twitchy.

Still, at least Mr Fallon’s intervention and the SNP’s adamantine-sounding “red line” attitude to nuclear weapons on the Clyde have raised the salience of the issue. Not since the 1980s has it been so debated now that the question of renewal is again live. Many, on both sides, feel passionately. For almost six decades, men and women of principle have marched, protested and been arrested because they objected to these immoral weapons of mass destruction. Now the SNP has slipped on the mantle of CND and that radical agenda.

Likewise, Conservatives and most, if not all, of the Labour Party, believe that nuclear weapons kept the peace after the Second World War and won the Cold War, and that they remain an essential part of Britain’s security in an uncertain world. Nuclear weapons have been no use to us at all in Iraq, Afghanistan, Sierra Leone or the Falklands, or against terror here and abroad. But the fact remains that future threats are, by their nature, “unknown unknowns”. If the first duty of every government is to ensure the security of its citizens, then a fully functioning nuclear deterrent comes before education, health, social security and everything else. So it is an equally clear matter of principle to them.

The truth is that defence is a practical problem, not a matter of ideology. A nuclear deterrent needs to deter, and not bankrupt the Treasury. The point about a submarine-based fleet is that a potential enemy never knows for sure where the weapons are or how many are ready to deploy. In that sense, it is sufficient to have a deterrent that is, to use that pejorative expression, “part-time” – one that is affordable to a nation so in debt as Britain, but also a power with a world role. Indeed, in a classic mutually assured-destruction scenario, it is sufficient for the enemy to fear that a nuclear weapon is probably on the high seas. Certainty is not necessary.

The UK’s nuclear deterrent will probably never be at the centre of things on its own. As part of Nato, and reliant on the United States for the technology, the British independent nuclear deterrent, as a British premier once almost put it, need not be British and need not be independent in order to deter.

It just so happens that this pragmatic “split the difference” approach is the one the Liberal Democrats advocate. No matter; it may soon be the one that Ed Miliband and Nicola Sturgeon find themselves adopting as well, whatever they say.