Tony Blair had the effrontery to attend yesterday’s service despite objections from families of the dead

Yesterday's service at St Paul’s Cathedral to honour the 453 British servicemen and women killed in Afghanistan gives us pause to reflect not just on their heroism and sacrifice but also on Britain’s foreign policy over the past 13 years.

One thing is beyond question; the 2001 invasion of Afghanistan, a direct response to the 9/11 attacks on New York’s Twin Towers, set off a chain of events that plunged the Islamic world into a new dark age and today threatens the security of every Western nation.

The reckless military adventures of second-rate Western politicians have created a generation of Muslim fanatics bent on revenge.

The human cost has been devastating. In Syria, 290,000 people have died in four years of war and four million refugees forced from their homes. And in Iraq – where Tony Blair took Britain into an illegal war based on a lie – 3,500 people are dying every month as Islamic State cuts a bloody swathe through the country.

Meanwhile Mr Blair (ludicrously made a peace envoy in the Middle East) continues to grow obscenely rich selling his services to tyrants and oligarchs while seemingly impervious to criticism of his role in this carnage. He had the effrontery to attend yesterday’s service despite objections from families of the dead. As one relative put it: ‘He cost all of those lives. He’s got blood on his hands.’

Almost as offensive as his presence was the calculated non-appearance of Scottish Nationalist leader Nicola Sturgeon, who snubbed the event despite the fact that 38 Scottish soldiers were among the honoured dead.

Elsewhere, Libya, ‘liberated’ from Gaddafi by Western intervention in 2011, has descended into an ungovernable swamp of terrorism and sectarian violence and even Egypt, once a beacon of power and stability in the region, is in turmoil following its brief flirtation with democracy.

But while we are rightly worried by IS and Al Qaeda, a much greater power – Russia – is engaged in military expansionism and defiantly sends its nuclear bombers to prowl the skies off Cornwall and Hampshire.

Truly, the world is in a fragile state. So what lessons can Britain learn from the past 13 years?

Firstly, we need to face up to the truth of where we went wrong. It is quite frankly a disgrace that after six years the Chilcot report on the Iraq War has still not been published. The ability of the establishment to look after its own can never be overstated.

Then we need to learn from our mistakes. It was a massive misjudgment by that ‘heir to Blair’ David Cameron to want to involve Britain in the Syrian debacle. It was only the collective common sense of Parliament that thwarted him.

Prime Minister David Cameron, pictured at Friday's service alongside Nick Clegg and Ed Miliband, must now commit to spending a minimum of 2 per cent of national income on defence in line with Nato guidelines

We must also accept that while nothing compares to the barbarism of IS, the West has compromised its own moral standing through the use of torture and incarceration of suspects for up to 13 years at Guantanamo Bay without trial. As we have argued many times, such tactics have acted as a potent recruiting sergeant for the terrorists.

But the greatest lesson we need to learn is that Britain must be prepared to spend enough on defence. Mr Cameron already stands accused of allowing the union to break up. He should take care that history does not find him guilty of destroying the Armed Forces at a time of great peril.

He must now commit to spending a minimum of 2 per cent of national income on defence in line with Nato guidelines.