This is the 5km grid Average Maximum Temperature for the UK on 10th August 2003 showing just SE England with Brogdale highlighted
(click in the image for a bigger version)
It can be seen that the Brogdale area is somewhat split off from the main area of higher temperature and a number of nearby cells are 2 -3 degrees C lower
As was mentioned earlier, this could be the effect of local topography and not an erroneous reading
This is Met Office data but they do not explain how these 5km cells are populated. They obviously include local stations in the area but here must also be quite a bit of averaging, projection and interpolation to get full coverage of the 10,000 or so cells which make up the UK