this one was roughly 12 by 14", each pocket was formed by stitching the front to the backing (from memory the backing was one piece but i only had a quick look), not like the lanchester pouches shown on a google search.
again it it similar to this sten? pouch but not the same. aka 6 pockets, mk1/2 pouch press studs, no carry sling, belt loops etc on the back.
think the lovechild of the pouch above and a US thompson pouch with some recessive early patt 37 press studs thrown in.