To judge by the way Moscow reacted to the latest allegations concerning its involvement in the Salisbury poisoning, it seems the Kremlin believes it can get away with just about anything – including the use of a deadly nerve agent on the streets of an English cathedral city.

That was certainly the impression given by the two GRU military intelligence officers when they appeared on Russian television to refute claims that they were responsible for carrying out the attack on Russian defector Sergei Skripal.

In what must count as the most unconvincing performance delivered in the history of modern espionage, the pair provided a laughable justification for their presence in Salisbury at the precise time the poisoning took place, claiming they had made the two-day round trip from Moscow purely to marvel at the spectacle of the cathedral’s 123-metre-high spire.

As the old saying goes, you can fool some of the people some of the time, but when it comes to this crass and clumsy exercise in seeking exoneration from such a heinous criminal act, the GRU men’s performance was totally lacking in conviction.

It is now said in intelligence circles that the only reason the pair made the television appearance was to punish them for breaking the cardinal rule of espionage – don’t get caught.

That said, I doubt anyone in the Kremlin or anywhere else in Russia’s sprawling intelligence establishment is unduly concerned by this turn of events. The likelihood of the two accused standing trial in an English court is zero and, from a Russian point of view, the mission was a success. The GRU might not have succeeded in killing Mr Skripal but it is very unlikely he will trouble the Russians again.

Nor should the fact that the intelligence agency has emerged as the main culprit in the Salisbury affair come as much of a surprise. An elite paramilitary unit within the Russian military, the GRU is the spearhead of the Kremlin’s global attempt to sow political discord and instability around the globe, with its primary target being western democracies.

The organisation has been implicated in seeking to influence the outcome of elections in America and Europe and dedicates a great deal of its effort to looking for ways to undermine western institutions such as the EU and Nato, which it regards as constituting a threat to Moscow’s global ambitions.

Apart from Salisbury, another of the GRU’s more audacious plots was its involvement in the attempted assassination of Montenegro’s pro-western prime minister in 2016.

The agency is also very active closer to home, especially in Syria, where it has been in the vanguard of Russia’s military intervention to prop up Bashar Al Assad. Working closely with their Syrian and Iranian intelligence counterparts, GRU officers have played a vital role in identifying and eliminating Syrian rebel groups.

And with the Syrian conflict in its final death throes, Russian President Vladimir Putin must have been quietly congratulating himself on a job well done.

Until, that is, this week’s disastrous incident in which a Russian Illyushin Il-20 transport aircraft was shot down by Syrian government forces using – irony of ironies – a Russian-made anti-aircraft missile system.

When I wrote last week that the uneasy alliance between Russia and Iran in Syria could soon spell trouble for Mr Putin, I had no idea that this would manifest itself so quickly, and with such terrible consequences for the 15 people on board the aircraft who lost their lives.

For the accident was the direct result of the conflicting objectives between Moscow and Tehran over their role in the Syrian conflict.

Russia’s primary goal is to prop up the Assad regime so that it can maintain its own military presence in the eastern Mediterranean. The Iranians, by contrast, see the survival of the Assad regime as an opportunity to broaden their military presence in the country, thereby enhancing their ability to confront Israel.

As the Kremlin enjoys a cosy relationship with Israeli Prime Minister Benjamin Netanyahu, the Russians have always had mixed feelings about Iran’s agenda.

And now, with the shooting down of one of their aircraft over Syria, the Russians find themselves caught in the crosshairs of the deepening hostility between Israel and Iran over the latter's growing presence in Syria.

For the Russian aircraft was shot down at the same time as Israeli F-16 warplanes were attacking a Syrian military facility near Latakia that the Israelis claim was being used by Iran to stockpile missiles ultimately destined for Hezbollah, the Iranian-backed militia based in southern Lebanon. The Syrians thought they were firing at the Israelis but instead managed to shoot down an aircraft belonging to their Russian allies.

Mr Putin’s discomfiture about the difficult position he now faces in Syria was evident in the comments he made following the incident, in which he sought to defuse tensions by stating a "tragic chain of circumstances" had led to the loss of the aircraft.

Despite the fact Russia and Iran are allies in Syria, Mr Putin has no desire to provoke a rift with Israel. For a start, many of the powerful oligarchs who keep him in power have Israeli citizenship and they would not take kindly to any fallout between the Kremlin and Israel.

Which means that, sooner or later, Mr Putin will have to decide between maintaining cordial relations with Israel or carrying on with his flirtation with the ayatollahs.

For a man who believes he can get away with anything, from using nerve agents on English streets to keeping reviled dictators in power in Damascus, Mr Putin is about to have a rude awakening.

Con Coughlin is the Daily Telegraph’s defence and foreign affairs editor