This is a dangerous moment. Donald Trump has once again intensified tensions with Iran and made our world less secure.

Whether in the next few days or the next few months, the situation could escalate dramatically.

In the face of a US President with his finger on the twitter-trigger, Boris Johnson must rule out, clearly and categorically, that if Trump takes the US into an armed conflict with Iran, the UK will not be dragged in with him.

Let’s just remember Iraq. And how we were pulled into the biggest US foreign policy mistake since Vietnam. And how the fires from that illegal war are still burning in Iraq, Syria and elsewhere. When Liberal Democrats opposed that war, we were heeding the warnings of British Intelligence – that the aftermath of an attack on Iraq would create a destabilising vacuum for Iranian militia, Al-Qaeda and other terrorists to fill. This time Britain must focus minds in the White House about the likely consequences if any military attack on Iran, as we failed to do so lamentably before, in Iraq.

In my three years on the National Security Council, the biggest decision I was involved in concerned Syria, and President Obama’s plan to respond to Assad’s chemical weapons attacks on civilians. I became convinced then that the highly limited and one-off attack on chemical weapons dumps, being proposed by the US, was right – both because the evidence and legal basis to justify the military action was sound and the strategy was measured, with the consequences well thought-through.

So I’m not against supporting military action that’s justified, in the context of a well-designed strategic plan. I am in no doubt: this Iranian regime is brutal. Soleimani was a dangerous man, with the blood of many innocent people on his hands.

Yet when we form foreign policy, the question is not one’s opinion of a regime or an individual. The policy question is: will our plan work and how do we best achieve security and peace in the Middle East and across the world?

The assassination of General Soleimani has made achieving that security harder. Trump’s decision to assassinate him was a reckless one.

First, because it increases the tensions. Second, because it will result in some violent reaction from the Iran regime and its sympathisers too. Third, because it consolidates the hardliners in Iran – helping them to unify their country, after a period of regular anti-Government protests. Fourth, because it has increased anti-US and anti-British sentiment in Iraq, and strengthened the influence of Iran there, which has grown in the years following the disastrous Iraq War.

Unfortunately, Trump’s serious miscalculation is now for the course with this particular American President. The Middle East had many problems when Trump came to power: the damaging repercussion of the Iraq War were still playing out violently in Iraq and Syria and arguably elsewhere too. Yet Trump had at least inherited a nuclear deal with Iran, and there were signs that engagement and diplomacy could bear fruit.

Yet Trump withdrew US support for that deal – despite criticism from Europe Leaders and the rest of the world. Trump has gone on to make up his foreign policy up on the hoof – or sometimes, it seems, on his not-so-smart phone.

As a result, Trump’s policies have been erratic, inconsistent and often incoherent too. Sometimes he says he wants to pull out American troops from across the region and leave the Middle East to it. Next he’s threatening to break international law and launch 52 missile attacks. One moment, he takes out troops from Northern Syria, enabling the Turkish army to attack Kurds in Syria. The next moment he’s threatening economic war against Ankara.

Britain needs to stand up to this Wild West approach to foreign policy. We could be the true friend of America, by standing up to Trump. We could assert ourselves, with European allies and others, and launch a collective diplomatic offensive rarely seen in recent years, to help this White House see sense.

Or we could continue with the current feeble approach. Wanting to be critical of Trump because it’s the right thing to do, but too afraid to do so, lest we offend him. Just because we need that trade deal.

The lesson from the Iraq War is – do what is right. However special you think the US-British relationship is, the right thing is to tell Trump the truth.