BIA is not cleared for 747's.
Largest cleared type is 767
Largest regular aircraft is 757
see
wiki 'Runway' paragraph.
Also European used to operate a small fleet of 747-200's out of Bournemouth which isnt that much longer than Bristol and if memory serves these were normally landed somewhere in the UK with longer runways for a refuel before departing on the long leg of the flight to wherever...
There is a youtube video showing a 747 take off from Bournemouth
here
A telephoto lens was used in the making of the video so everything is a bit foreshortened but even so it looks a bit marginal...