The only other group of scumbags capable of planning and carrying out this attack would be the IRA. In Blair's statement he said an Islamic group carried it out and went on to say that the vast majority of Muslims are peaceful and will condemn this. The timing of the attack at the start of the G8 would indicate the later rather than the former.
I'm afraid we will all just have to be more vigilant in the future. Hopefully this doesn't lead to suspicion of everyone asian/arab etc.
Like Hitler and the IRA these Al-Qaida loons don't realise that this act will just make us more resolute.