Love the bag fits me easily. This will be an awesome 2 season bag for me. This is my first british army modular bag purchase so I went for the light bag with a view to getting the medium bag later. The theory is the lighter bag fits and can be tied into the medium bag by design to make a 4 season bag.
So I thought the sleeping bag liners would fit and tie into the inside of both the light or medium bags. I was wrong. The light bag doesn't have the tie points inside for the liner.
The liner appears to be a liner for the medium bag only if you want it to be tied into position. It's a case of use the liner or the light bag and a loose liner as far as I can see at the moment. So it will fit etc in the light bag but as a loose liner.
Live and learn. This is not a criticism of the light bag. It is awesome. Just some info if you are buying the modular system slowly over time.