Proving criminal responsibility can be a complex business. Especially when it comes to murder. A cool head is required, standing back and not being swept along by emotion. There must be a deep respect for the rule of law without bypassing due process.

So how is the UK standing up to these tests when it comes to the appalling attempted murder of a former Soviet spy and his daughter using a rare nerve agent? I refer, of course, to Sergei and Yulia Skripal.

So far the evidence points firmly at Putin’s Russia as the source of the mischief, whether through the Russian state losing control of ex-Soviet chemical weapons or deliberate policy. In either scenario they would be responsible. The problem is that, so far, the UK government has not proved its case definitively, beyond stating that experts believe the nerve agent originated in Soviet Russia and was inherited by the current regime.

Last week I felt saddened by some of the prematurely bellicose posturing of our political elite. It felt as though there was something cynical about their response, as though they hoped to benefit from this crisis politically rather than tackle a complex situation in a pragmatic way.

Yes, they were prepared to expel diplomats and deploy the grandest rhetoric, but no, they were not prepared to take any measure that might seriously affect Russia’s billionaire oligarchs who use London as both a playground and place to launder their millions.

Now is an especially good time for a national reality check. Britain is not a military superpower. Indeed, since 2010, the government has cut defence spending from £42.5bn to £37.3bn. It only makes our nation look ridiculous on the world stage when Gavin Williamson, the Defence Secretary, tells the whole of Russia to ‘shut up and go away’.

A more statesmanlike approach would centre on the use of multilateral co-operation to seek justice for this incident and to further our foreign policy aims.

Which brings me back to the importance of due process when investigating a crime. The police themselves have stated it will take months for a definitive conclusion, let alone the possible conviction of criminals in a court of law.

If we have learned nothing else from notorious miscarriages of justice like the Birmingham Six and Guildford Four, who were falsely convicted as IRA bombers, slow “good” justice is far, far preferable to swift “bad” justice, however satisfying the latter might feel.

Evidence should always be at the core of sound foreign policy. The on-going horrors caused by the illegal war in Iraq remains proof of that. The Iraq conflict was justified by politicians at the time in a similar overblown and emotive style we witnessed on our TV last week. With regard to Iraq they were citing ‘reliable intelligence’ of Weapons of Mass Destruction that afterwards proved to be politically-motivated fiction. In addition one could mention David Cameron’s misjudged military adventure in Libya that has caused so much pointless misery for the ordinary people of that region. It is not helpful to label anyone who does not wish to run ahead of the facts as a “traitor”.

We should also be mindful that the UK, along with 192 other states, has signed the Chemical Weapons Convention that is overseen by the Organisation for the Prohibition of Chemical Weapons (OPCW). This is the same organisation awarded the 2013 Nobel Peace Prize because “The conventions and the work of the OPCW have defined the use of chemical weapons as a taboo under international law”.

If international law is to help us secure truth and justice we must follow internationally agreed procedures for investigating chemical attacks, as set out in our treaty obligations. Above all, we must work closely with the UN and keep on having those difficult, frustrating conversations with the Russians and our allies that are at the heart of diplomacy.

Democracy is a system built on moderation, tolerance, debate and evidence-based thinking. If we forget our core values while confronting this appalling incident, the perpetrators will have poisoned more than just their victims.