IO and others.
the idea that there is a lot less traffic at say 3000'+ can be a questionable assumption. This may be true of powered light aircraft but on a thermic day the gliders will operating as high as they can keep themselves. ie from cloudbase to 1000 - 1500 feet below cloudbase. So if it's a 5000' cloudbase day, there will be a lot of gliders in the 4000' band, particularly through the known choke points.
Sad to say Didcot/Abingdon is one of the said choke points