Ian is uploading a series of videos covering development of SA80/L85
In the first video he goes over mock ups
Armament Research (part 1): http://armamentresearch.com/british-enfield-sa80-part-1-mock-ups/
It's interesting to hear that Brits selected 4.85mm caliber and considered bull pups to be a good choice with straight stocks.
There always has been attempts to design rifles so that it can act as both infantry issue weapon and support weapon.
Then came the firable XL60 series
Armament Research(part 2): http://armamentresearch.com/british-enfield-sa80-part-2-xl60-series/
It's interesting to note that none of 26 engineers had shooting experience. It does take user feedback to make good product.
Armament Research(part 3): http://armamentresearch.com/british-enfield-sa80-part-3-xl70-series/
Tales of problems are abundant which was later fixed by H&K and issued as L85A2
From: Forgotten Weapons