I went to what I was told at the time was the old Naish hill with some Bath Motor Club friends in the 1970s. The course was mostly unsurfaced but did have concrete or tarmac (can't remember which) at a couple of the corners. I'm fairly certain we went in via a track past Naish House. Aerial View Naish Hill© Multimap Naish House in the bottom right corner (SSW) and then on upper right hand side of the picture you can see a lazy S with two hairpin bends with the course defined by a few trees or scrub along its length.Naish Hill
The site of the first timed speed event by the RAC after World War II, Naish Hill was used in August 1945. The road was loose surfaced, and is now the link road between the B3128 and the B3124 to the south of Clapton in Gordano (west of Bristol and south of Portishead). It is named after the nearby Naish House. from Great Britain & Ireland Hillclimb Venues

Dick Pease in the Bearspeed Ford Escort exits one of the hard surfaced hairpins
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You can just see part of the hillclimb course as you pass on the M5 (which you can also see in the aerial view) but its better not to try if you are driving

Have I got the right place?
Does anyone know what length the hillclimb was?