SMLE - there's a good few of them in Afghanistan, only problem is the wrong side have them
The sa80 family and 5.56 do the job they are designed to do, and you can carry much more 5.56 then 7.62
The only problem with bringing up ar15/m4 etc as the solution platform is the default ammunition is also 5.56, so that loses the stopping power argument. (Though there are other ar15 styled weapons in other calibres - standard ar15 based weapons are 5.56, others for other jobs are other calibres)
A variety of weapons and an associated variety of calibre according to role, are the solution and are in use
The sa80 family & 5.55 are the standard, most but not all will carry that. Any group will have an appropriate mix of capabilities and other resources to call upon
If doing a different task then you take other equipment
We have a number of mixtures of items, some due to doctrines and are standard, some are UORs to meet requirements on the ground.
We won't be in Afghanistan for much longer (relatively) and will be doing other things afterwards.
When everyone has come home then decisions get made as to what happens to the UORs. They could be dropped or may go into the cupboard.
Bear in mind that irrespective of Afghanistan, Iraq etc that the GPMG was replaced long ago by the LSW, but people had some common sense and the GPMG remained. There was a perceived gap in capability if the LSW was allowed to replace the GPMG