I'll be on the 0720 to Madrid in the morning. This story's got a long way to go yet.

From the start, the extent and scale of the this morning's bomb attacks made many of us suspect that terrorists other than ETA, or working alongside the Basque separatists, must have had some involvement.

It's still too early to say who was behind the attacks but there are several competing theories:

1) A crack down by the authorities has given birth to a new, younger and more bloodthirsty leadership within ETA, which is more prepared to use indiscriminate force (perhaps "inspired" by the likes of Al-Qaeda.)

2) The blasts were a joint operation between ETA and Al-Qaeda, the two organisations forming an alliance in order to cause mass destruction.

3) The blasts were the work of Al-Qaeda alone -- the co-ordinated explosions, Spain's support for the War in Iraq and the fact that AQ cells have been uncovered in Spain in the past all lend weight to this theory.

Of course, if it could happen in Madrid it could happen anywhere in the world. Britain's police and intelligence agencies must be increasingly nervous.