OS shows the height of this Trig point to be 315.8216m ODN and 0.03m above ground level according to the last time it was verified in 1956.
More details from Ordnance Survey - National GPS Network - Staion Name and Number (Walton Hill - T1SO9479)
There are a number of Geocaches in the area you could do at the same time and this trig can be logged as a Virtual cache on 'Ye Ole Survey Monuments' as YSM051.