I venture to suggest that for an area to qualify as a "clearway" it has to meet the ordinary meaning of that word, i.e. a way which is clear and unobstructed. As appears
from Google maps, in the direction of takeoff on RWY 27 there is indeed a clear and unobstructed area of grassland beyond the runway that appears to meet the description of a clearway. Once the lights/fence/road is reached it is no longer a "clearway' because it is obstructed.
Does that area of grassland stretch 1000 metres beyond the runway?
The lower limit of a clearway is defined by a slope angle (ISTR 1 in 60 but ICBW) which assumes a minimal angle of climb. Bristol is on a hill and the ground beyond 27 falls away rapidly. All you need to do is clear the
ILS antennas.