The small triode on the right has the grid at right angles to the pentode grids. The screen grid connection is made at the top with a support seen in the foreground.
This valve is an import but Mazda are part of the BVA.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 41 mm tall.
References: Data-sheet & 1040. Type PCF801 was first introduced in 1963. See also1963 adverts.