“I would like to applaud your initiative in taking this forward,” Mr Blair told his Spanish counterpart, José Luis Rodríguez Zapatero.

“Resolving these very long-standing issues is difficult work, but you’ve just got to keep going,” he said, recalling his own experience negotiating the Good Friday peace deal in Northern Ireland.

He said that such talks were “difficult to do” but “always right”.

Spain’s Socialist Prime Minister has faced an onslaught at home from the country’s right-wing opposition, which believes the Eta negotiations are tantamount to surrender in the war on terrorism.

Among the staunchest opponents of the talks are Mr Blair’s good friend, José María Aznar, who sent Spanish troops to Iraq when he was Prime Minister.

Señor Zapatero said he had sought advice from Mr Blair on the Basque peace process during their talks yesterday. “His experience has been very useful to me,” he said. “I want to thank him publicly for the support of his government during a difficult process.”

Six months after Eta declared a “permanent ceasefire” in its 38-year violent campaign for Basque independence, the peace process has stalled and there are growing worries the group could return to violence.

Hooded gunmen appeared recently at a separatist rally, reading out a belligerent statement and firing into the air. Others have torched buses and cash machines in the Basque country.

The overheated rhetoric and images of burnt-out vehicles have served as a potent reminder for Spaniards of the convulsions of yesteryear.

Eta has killed more than 800 people over four decades in its violent campaign for a Basque homeland straddling the border between Spain and France.

In recent years, however, it has been greatly weakened by arrests in both countries, and has not killed anyone in more than three years. Public revulsion at the March 2004 Madrid train bombs, the work of Islamic extremists, is also thought to have contributed to Eta’s decision to end its campaign of terror.

Mr Blair’s relationship with Señor Zapatero got off to a rocky start in 2004 when the Socialist leader pulled Spanish troops out of Iraq, fulfilling a campaign pledge.

But despite their disagreements over Iraq, the two centre-left politicians have much in common and diplomats say they get on well. The two spoke often last year during the British presidency of the European Union, especially during the tough EU budget negotiations.

The two leaders have previously discussed the best tactics to use in their respective efforts to end two of Europe’s longest-running conflicts.

In an interview in July with The Times, Señor Zapatero said that he would be approaching the talks with Eta “very cautiously and discreetly”, adding that “they are two pieces of advice that Tony Blair gave me”.

The Spanish government has also been highlighting what it claims is the key behind-the-scenes role played by Mr Blair getting the Basque peace process to this point. British sources have played down the extent of his involvement.

Both leaders said that the European Union should take a greater role in securing its borders against illegal immigration, as well as working to improve living conditions in the countries they flee.

In the past year, more than 25,000 Africans have travelled in rickety boats to Spain’s Canary Islands in journeys of 1000 miles or more. Thousands more are thought to have died in the attempt.

Mr Blair is today meeting 16 top Spanish and British businessmen. Spanish companies like Telefónica and Ferrovial have spent tens of billions of pounds in the past few years buying British companies like BAA and O2.

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