In a nutshell, this was an attempt to emulate the US ALICE system by re-hashing '58 in nylon. Fair do's - it was an honourable undertaking - and perfectly sensible, considering there was much controversy about the unsuitability of absorbent materials (cotton webbing) in an NBC environment. It was thus better proofed against liquids - ergo easier to decontaminate. Brilliant!
The only snag was that the butyl material used in the construction used to make the whole rig fall out of adjustment when placed under stress, i.e. running with full pouches. It was a faff. One good thing happened as a result of these trials and that was the introduction of the nylon Para/SAS Bergen (in lieu of the old canvas A Frame still in use in the early '70s) and the nylon S6 respirator haversack - which is still in use to this very day (prior to this, the inferior canvas '58 pattern haversack was in use).
1972 pattern equipment was trialed by several units, but was rejected in favour of the trusty '58, which soldiered on until the advent of PLCE in the 1990s. A nylon version of the '58 pattern kit was tried but was dropped due to costs. This is sometimes confused with the '72 gear. Some of these nylon '58 pattern items can be sourced at Silverman's.
A revised pattern assault vest was trialed in the 1980s. This is a Mk2 version of the '72 pattern assault vest - images of which can been seen in This is the SAS by Tony Geraghty (inside cover). The pouch closures are the same as ALICE webbing, with 'two prong'-type fastners on the '80 pattern. The '72 pattern Mk1 used metal fasteners. Great for stabbing your thumb if you are busy.
Kit anoraks might be interested in Martin Brayley's books on webbing, available through amazon.co.uk. However he stops at '58 pattern.
As the images of this webbing are RARE, Here is a gallery.