Solid gold combo from the well known London jewellery firm of Watherston & Son (Makers to HRH the Prince of Wales). Similar to many American designs, with the telescoping inner barrel, but with a barleycorn pattern rather than the more common fluted design. I suspect that Mordan, or another reputable London maker was the actual maker of this item as I cannot find any reference to Watherston having made writing implements. Likely late 1800’s as Watherston & Son were in business from 1864-1911.
Watherston & Son