|Liberty & Co, London, royal warrant holder|
If your ancestor served the royal family in some way there is a good chance that there will be a record of it somewhere. Some records of people were employed in the royal household might be held by the Royal Archives at Windsor Castle, although earlier records are more likely to be at The National Archives.
There are online research guides Royal household and wardrobe before 1660, Royal Warrant holders and household servants and Royal warrant holders and suppliers of goods after 1600.
I am particularly interested in the second and third of these guides, because they deal with references to shopkeepers and others who supplied goods to the royal household. A household of that size has always done a lot of consuming, much of it from regular suppliers; just think of all the places where you shop and how much you spend there, then multiply it by a large number (depending on the size of your family and how rich you are), and you will see that an awful lot of businesses must have sold goods or services to members of the royal family over the last few centuries.
One of the sources referred to in the guides is the London Gazette, where annual lists were published from 1900 onwards. Part of the list from 1905 is shown below; the entire list occupies 21 pages. It includes well-known businesses like large London department stores, but also businesses of all sizes from all over the UK and even further afield. Some of them are small shops near royal residences such as Sandringham, Osborne, Windsor and Balmoral; so if you discover an ancestor who ran a sweet shop or a dairy in one of these areas about a century ago, the London Gazette might be worth a look, you never know your luck. It's free to search and dowload - one of the best bargains in family history!