Not sure where you got this from, but for most of WW2 the British squad was a 10 man affair, with an NCO armed with a SMG (Thompson, then later Sten), 6 riflemen (with SMLEs and then N04s), 1 Bren Gunner, 1 No 2 on the Bren plus an ammo carrier - both armed with a rifle. No British infantry unit to my knowledge ever had more than 1 Bren per squad - am not 100% sure re the Airborne, but will check and post again.
Sorry Sommecourt-you would know better than me. My knowledge is only based on several photographs...I made the mistake of assuming this was therefore common practice...