Potteries Brick Co Ltd D

A bit of a mystery behind this brick as I have been unable to identify the location of the brickworks or even the correct name of the company. Bricks of this sort lettered 'P B Co Lt' and with a further letter, 'D' in this case, are very common across North Staffordshire and south-east Cheshire. The sheer numbers suggest a substantial operation, so does anyone know who and where?

Answer finally provided through great research by Capitol 203 who found a list of brickworks made in 1943 by the Ministry of Supply. This makes it clear that the Potteries Brick Co. Ltd acted as a selling agent for at least eleven brick companies in the area. The assumption is that each brickworks used a different letter on their bricks, but all stamped them with the PB Co label.

The works involved in 1943 were:

Beans Brick & Marl Co, Tunstall
Berry Hill Brickworks Ltd, Fenton & Cheadle
Birchenwood Brick & Tile Co Ltd, Kidsgrove
Cobridge Brick & Marl Co. Ltd, Cobridge
D. Duddell, Fenton
J. Hewitt & Son (Fenton) Ltd, Fenton Low
J. Leigh & Sons, Burslem
Wm. Palmer, Exors of, Cobridge
Sneyd Collieries Ltd, Burslem
The Stafford Coal & Iron Co. Ltd, Great Fenton
Thos. W. Ward Ltd, Apedale, Chesterton