A mildly useful length of nylon strapping with a clip fastener that allows you to fasten and tighten said strap. Good for tying things to other things. Seem to have been specified by a cost-conscious member of MoD(PE), because they're always the absolute minimum possible length for the job at hand, especially when it's dark and your fingers are cold.
Usually found in a sealed plastic bag in the QM's store, alongside the big bag of issue Bungees, because if they were issued, they'd have to be checked. And lost ones would have to be demanded. And that would make life more difficult.
Still, they're an improvement over the 58 pattern utility straps (which were like rocking-horse shit by the 1980s) which added "made of canvas and bloody awkward when wet" to the "never quite long enough" design flaw.