Those are Thompson submachineguns, the famous Tommy Gun, just seen from an unusual angle.

Britain imported large numbers of Thompsons until the Sten Gun entered production in 1941 (and then afterwards as well). In a typical rifle section, SMGs were usually issued to the section commander. That there are two men carrying Thompsons in this picture suggests that one might be a member of the Platoon Command section, who has dropped in with this rifle section.

Kennedy, Organization of the British Infantry Battalion 1938 to 1945

War Establishment Table II/233/3, 1944, War Establishments.

For further specification, the weapons the first three men (it is an odd angle but the third man in line is also holding one) are Thompson M1928 Sub-machine guns.

This variation of the Thompson was the first military variation. There were later military variations but given the background on the picture, there are a few clues that lead us to the conclusion that it is not another variation such as the M1928A1, M1, M1A1 (three subsequent variants that look similar to each other but are distinctly different from the M1928). The distinct identifiers are:

• The Barrel. There is a lack of a straight fore grip and a tapering effect on the barrel (which is distinct to the M1928). This image illustrates the difference between the M1928 and the M1928A1, (with the M1928A1 being on top, and the M1928 on the bottom)
• The position of the third man's hands confirms the existence of a regular fore grip (you can just about make out his left hand holding it)
• The Compensator. This part of the barrel just beyond the end sight on the barrel was exclusive to the M1928 and M1928A1 only (it was removed on later versions such as the M1 and M1A1 as it was too complex to manufacture).

Citation: Bishop, C. (2016). The illustrated encyclopedia of weapons of World War II: A comprehensive guide to weapons systems, including tanks, small arms, warplanes, artillery, ships, and submarines. London: Amber Books.

EDIT: Wording and added citation