The onus if any rests with the owners/operators of the airfield (MOD) as it is a known issue (there is a link to last year's near miss with a Typhoon in another part of Pprune).
If all they can appear to do is erect warning signs then it is highly likely that this is the only legal option open to them.
From another POV it could be said that the onus actually rests with the owners/operators to ensure that aircraft are not, normally, permitted to fly that low on the approach at that location