Having researched further, looking at old catalogues, it seems it's a WHS Halo System 10 (pre Veka's ownership of Halo and development of System 10 - Veka System 10 uses a different bead).
https://web.archive.org/web/20061231103354/http://www.whs-halo.co.uk/files/sys10brochure.pdf
Appreciate...
Hi, we're missing beading around our window. There are two bits already there holding it in top and bottom - but obviously want to fully bead it in. Have spent several hours on this this morning trying to figure out what bead we need. Window frame says WHS Halo and I've looked at their...