You'll probably be OK anywhere off Preston Road - try around Surrenden Road - you can walk to London Road station and get the train back to the centre, about 2 minutes or get a bus from Preston Road.
IF it is al-quaida - theyve got a few hundred troops in Afghanistan and a 6 bombers invlved in the Lybian situation. Not a lot really, but maybe they were seen as a 'soft' target.
The labour party rally seems a bit left field for Al-Quaida though