Apparently it was introduced into United Kingdom in the 1930s by the Maclean's Company, which was subsequently taken over by the Beecham Group, and eventually by SKB.
Yesterday I bought a new tube of Maclean's and almost immediately noticed that the royal warrant was missing.
This warrant was a conspicuous likeness of the Prince of Wales' feathers, surmounted by the legend: By Appointment to HRH The Prince of Wales, Suppliers of Toothpaste, GSK Consumer Healthcare. Brentford, Middlesex.
Evidently another concoction is used to clean the royal gnashers now!