It's unlikely to be the "large BBC mast". The BBC HF transmitter site at Daventry was closed and demolished back in 1992 or thereabouts. The only BBC mast left at the site is the old 648kHz MF vertical at Dodford, which if I recall correctly is used now for Radio Northampton and some commercial services.
According to the current RAF BINA, the VOR is at 52N10.81 001W06.83. AutoRoute puts this location about 1.5nm east of the Dodford mast. If DTY is a Doppler VOR (it sounds like one from here) it should be easily visible from quite high altitude on a clear day.