There are two current Mid-War books, both of which cover the same time periods of 1942-1943. They both cover Allied and Axis forces.
Afrika covers forces in North Africa and the Mediterranean. It has lists for German, Italian, British and Commonwealth (which includes Irish, Scottish, Indian, New Zealand and Maori, and South African forces), and American forces.
Ostfront is the other book, and it covers the Eastern Front. It has lists for German, Hungarian, Romanian, Finnish, and Soviet forces.
So if you want to run a Mid-War British rifle company, Afrika is what you need.