Does anyone know a non-internet sourse of neutral cure silicone
sealant? In/near Glasgow? I asked in Thomas Graham and the man had
clearly never heard of such a thing.

The shower trap I am fitting says to put only neutral cure silicone
sealant between the flange and the shower base since acid ones can
attack the flange. The flange is chrome plated plastic so this sounds
like a wind up to me.