As the world reels from the Nice massacre, on Monday parliament should be expressing our solidarity with France and discussing what we need to do to protect our own citizens from similar attacks. We should also be debating how to stop Turkey’s government using the weekend’s events as justification to increase repression of free speech and democratic opposition.

But instead, the government will spend Monday turning national security into a political game. A seven-hour debate will be held, not to ask parliament what should be done to fight the current threats of extremism and instability but on whether, in principle, Britain should have four new nuclear submarines ready to use in 30 years’ time.

There is nothing new in this debate – a vote in principle was agreed in 2007 – and nothing whatsoever will happen as a result. It doesn’t authorise any new funding, or establish any new mechanisms for the delivery or oversight of the programme. It is being held simply to sow further divisions inside the Labour party. The Tories know that those with strongly held principles on either side of this debate will vote with their consciences, and the media will turn the event into a fresh Labour crisis.

At any time, that game-playing would have been shameless; after Nice and Turkey, it is shameful. Even the Tory chair of the Commons defence committee has described the playing of politics with this long-delayed vote as “beneath contempt”. And at a time when nationalist feeling in Scotland is already inflamed by Brexit, Monday’s vote is not just shabby and pointless, but reckless. Anyone who wondered if the government would behave differently with Theresa May in charge has got their answer. Indeed, the new prime minister has personally chosen to lead the debate.

Labour should not play this game. We should treat this government and this vote with the contempt they deserve. Moreover, there are clear principled and practical reasons why Labour MPs should refuse to vote with the government on Monday. They propose an open-ended commitment to maintain Britain’s current nuclear capability “for as long as the global security situation demands”. Such a vague, indefinite commitment precludes any possibility of Britain ever stepping down the nuclear ladder and contributing to global multilateral disarmament.

Labour has always believed fiercely in ridding the world of nuclear weapons. When Nye Bevan famously demanded in 1957 that he not be sent “naked into the conference chamber”, he was not championing nuclear weapons. As he said in the same speech: “It is not a question of who is in favour of the bomb, but what is the most effective way of getting the damn thing destroyed.” The same principle drove Harold Wilson to negotiate the nuclear non-proliferation treaty in 1968, and drove Margaret Beckett to announce a series of concrete steps towards “a world free of nuclear weapons” alongside the Trident vote in 2007.

In other words, Labour has always believed that maintaining nuclear weapons for the medium term must go hand in hand with efforts to eliminate them for good. This motion moves sharply away from that principle.

In practical terms, we are also in the bizarre situation where the government is asking parliament to approve the new submarine programme, but refusing to disclose the total costs of that programme. At the latest, rapidly increasing estimate, manufacturing the subs alone will cost up to £41bn. To put that in perspective, the total cost of Britain’s military interventions between 1990-2014, including both Gulf wars and Afghanistan, is estimated at £34.7bn.

These cost issues are even more worrying given the financial impact of Brexit. While some argue that it doesn’t matter how much Trident renewal costs, it clearly will matter if our already highly stretched conventional defence capabilities must be cut to pay for it.

If we choose to retain a nuclear capability, there are many cheaper alternatives than building the full complement of replacement submarines, but they have never been seriously explored under any government.

Our current Labour defence review is exploring those options and how we would evaluate them, as well as looking at what concrete steps we could take towards global multilateral disarmament, and ensuring that the jobs and skills provided within the UK nuclear defence industry can be retained in full.

That sober, rational analysis is informed by contributions from thousands of party members, hundreds of constituency parties, several MPs, countless experts and all the major manufacturing unions. That will lead in due course to a democratic process to decide our policy for government.

That work will continue regardless of Monday’s parliamentary pantomime, and it matters far more than what lobby MPs choose to walk through in a vote that means nothing. For that reason, we will be abstaining from this ludicrous exercise, and getting on with the real job instead.