Belt fed mg means you become more like German squad whose sole rationale was to carry ammo for the mg34/42 - I stand to be corrected but think that 1 Bren per section works ?
If you really want to go down that route then was there a bipod besa ? ( I know it's different bullet so crap logistics as Bren uses same as the smle.
How about Vickers VGO for your assault group much higher ROf - was used by RM at d day as SAW
In another thread I discussed the evolution of the Squad (Section) and how it runs either rifle centric or machinegun centric. The Germans concluded from WWI that the firepower of their squad was to be built upon the machinegun and it needed a high ROF to achieve any hits at what was assumed to be only fleeting targets. The rifleman became supporting fire in this mindset, longer ranged, accurate, and more often than not simply to protect the MG crew (and bear ammo).
The USA moved rifle centric with the Garand showing the reliance upon massed rifle fires to prevail. I think the Germans were ahead of the curve for the ear and ideally one adds the semi- (or full) automatic rifle to bring us to the modern era. My opinion would be that Britain was rifle centric, the BREN is more a supporting arm than the real firepower of a MG, you move up to find the base of fire of MG in British units like American infantry. This is entirely doctrine driven, you need to find a different mindset to pursue a MG at Section level for the British Army, it came with wartime experience and opposing German infantry structured this way. I think the VGO would have been a great stepping stone in that evolution but again you need someone changing how British infantry fight to compel a change in procurement. This impacts the SMG also.
The Germans introduced the MP40 as the logical extension of its trench sweeping lessons from WWI and it added close in high volume fire for clearing houses, taking a hedgerow or just adding din and furor to the engagement. British Army did not book the same lessons and seems uninterested in adding a SMG at Section level until war came and it hurriedly bought Thompsons and developed the Sten. Again one needs to find the doctrine change to set in motion adoption of a similar mix of weaponry as one sees in German infantry and latter in US as well as British where at least one SMG is carried to compliment the riflemen in assaults.
From WWI it seems obvious that machineguns, grenades and mortars are the killers with SMGs very useful, rifles being specialist weapons. We see something along these lines in proposals to ream the US Army Squad after years of urban warfare in Iraq. The British Army after WWI returned to a policing the Empire paradigm that also shades doctrine and weaponry. The disability is that arming to fight the last war sometimes comes up short. We see the arguments regarding British armour doctrine, so one needs to reason how far the lessons open horizons. I am partial to the German model in this era, it has a lot to commend it. The British Army had no shortage of experience or thinkers, perhaps as it pursued more mobility and doing more with less lads it might have pursued a GPMG sooner and more deliberately.
