The Madrid bombings were the first big al-Qaeda-inspired attack in Europe and shattered any illusions that the threats of Osama bin Laden were mere empty words.

Three days later the Spanish Government, which had been targeted by al-Qaeda and its allies because of its involvement in Iraq, was swept from office at the polls. Spain was unprepared to deal with the Islamist threat. In the immediate aftermath the Government blamed Eta, the Basque separatist organisation.

Although the hijackers responsible for the events of September 11, 2001, had been in contact with extremists in Madrid, there were only 65 Spanish police officers or intelligence agents assigned to countering Islamist terror.

March 2004 taught Spain the harsh lesson that France and Britain had already taken on board - the threat was real and within their own borders.

But Britain also learnt harsh lessons, and one of them may have contributed to the shooting of an innocent man at Stockwell station a year later.

The initial alarm call in Britain had sounded more than a year before Madrid, when police uncovered an attempt by terrorists based in Finsbury Park mosque to make ricin and other poisons. Kamel Bourgass, the ringleader of that cell, stabbed Detective Constable Stephen Oake to death in Manchester during an attempt to avoid arrest. The ricin plot ended any thoughts that Islamists would not carry out attacks in Britain.

But if Britain was ahead of Spain, it still recognised that lessons could be learnt from the events in Madrid. The bombers had shown a level of sophistication not yet seen in Britain, using mobile phones to detonate remotely devices on crowded rush-hour commuter trains. When they were finally surrounded in a block of flats, the terrorists had blown themselves up in a further attempt at mass carnage.

That suicidal act had important reverberations in Britain. Operation Kratos, the shoot-to-kill policy for known bombers, was devised and the strategy for confronting suspected suicide attackers was overhauled.

The aftershocks of Madrid were to be felt on the streets of London as police began a manhunt for the July 21, 2005, bombers. In the days that followed an innocent man was shot dead after being mistaken for a bomber. Then on July 29 police surrounded a block of flats in North Kensington after finding one of the bombers.

“If escape was not an option for him our biggest fear was that he would detonate an explosion to take us and himself out,” a senior firearms officer said.

“We had all been aware of Madrid and we had all seen the footage.”

Britain learnt from Madrid, made mistakes, then tried to refine the lessons. The most important lesson of all is that, when the enemy is global, any incident, wherever it occurs, can shape the antiterrorist response in every threatened country.

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