The explosion occurred outside the offices of the Spanish infrastructure group which owns Heathrow, Gatwick and a series of other British airports within the BAA group. The company was targeted because it is involved in building part of a high-speed train link through the Basque Country, which is to join the rest of Spain and France.

Authorities had plenty of time to evacuate the area. A telephone warning was made to the Red Cross before 8am saying, “I call in the name of ETA - we have planted a car bomb in the Calle Ribera del Loira next to the Ferrovial-Agroman building which will blow up at 9am.”

ETA has threatened many companies and their workers involved in the rail link. In December, businessman Ignacio Uría, was shoot dead by ETA as he owned a construction company working on the rail link.

Today’s attack was the first in the Spanish capital since the attack on Madrid's Barajas airport in December 2006. The latest attack follows yesterdays Spanish Supreme Court ruling banning two separatist political parties, Askatasuna and Democracia 3 Millones from standing in Basque regional elections which take place next month. The court ruled that both were fronts for ETA which has been ruled an illegal organisation.

The 40 year campaign for an independent Basque Country in northwest Spain and southwest France has killed 825 people.