Close thing h-r, but my 2005 Pooleys has:
Dunkeswell: 839 ft
Huddersfield (Crosland Moor): 825 ft
Interestingly, I had been hoping that Oban would be the lowest - but Pooleys has it at 20ft AMSL and there are a couple lower - including Glenforsa at 15ft. Does anyone know if there's any lower than sea-level in the UK ?