The information from the National Archives gives their service address as 11-13 Bream’s Buildings, London E.C.4 and 26-28 Bedford Row, London W.C.1
It is interesting to note that Sanderson & Co is a service address that comes up a few times with both Duron-style pieces and broader ornament and personal items.
Listed here are more details (as I find them) of companies that used this company at some point;
Herbert Löhnberg. After Herbert and his father, Max, had been using A.W.M. Faulkner & Co as their original service address (from what I can see). Herbert then moved to this new company between August 1958 and January 1959 during which time he became the sole registrar.
Raymond Jacobs, who were based in East Topping Street, Blackpool, used this service address around August 1959 when they applied for two design registrations (Reg. No 894270 and 894271) on “table or mantel ornaments”. Sanderson & Co was now at 26-28 Bedford Row, London W.C.1. Note: they may have applied for other pieces before or after.
Gilda Jewellers Ltd, who were based in 34-35 Hatton Garden, Holborn, London E.C.1, had registered jewellery (charms, lockets etc.) and applied for registration in January 1960. At this time the service address for Sandersons was still Bream’s Buildings.
Kenneth Chidley, who was trading as Clifford & Chidley, Warstone Lane, Birmingham in February 1961 also registered several finger ring designs and used the Sanderson service address in Bream’s Buildings.
Around the same month, Jay & Bamford Limited, based in 83 Goswell Road, London E.C.1 were also designing finger rings and using Bream’s Buildings.
More research to do here, but maybe this was a cooperative society??