This is a Marconi Q valve, the first hard vacuum valve produced in the UK.
The most striking feature of this triode is the wire mesh cage grid. The grid is made of longitudinal wires with interwoven helical wire and all supported on a rectangular wire frame. The filament is not clear but appears to be a single strand filament running the length of the valve and tensioned by a spring. Seen on the right of the picture within the grid cage. The anode is a plane metal cylinder taken to one of the side connections.
The thin glass tube envelope is 15 mm in diameter and, excluding the base pins, is 70 mm tall. Across the side pips measures 23 mm.
References: 1003 & 1005. Type Q was first introduced in 1916.