Pilgrim Payne of Latimer rd London W10 are the royal warrent Holders, though in practice work is allocated by whoever is dealing with a particular job and they are not required to use the warrent holder.
Over the years I have done quite a bit of work(fitting not cleaning) for the royal household, but not so much in recent years as my contact there retired and I supose the new man has His own prefered contractor.
The first job I did was for Her royal Highness The Princess Margret, Countess of Snowden (decesed)
I remember waiting for the check to come with great excitment to see who had signed it( Iwas thinking of hanging it on the wall) In fact it was signed by the Comptroller( thats right with a p) of the Queens household.
So I banked it
Michel