Buckingham Palace is unable to clearly say which members of the royal family are patrons of which charity, according to research by the charity consultancy Giving Evidence.
The research found that the information held by Buckingham Palace was "inconsistent and incomplete, and very confusing", and concluded that any figures for the number of charitable patronages given in the press were probably wrong.
The royal family’s website offers users a drop-down menu next to each royal showing which patronages they hold, but Giving Evidence found these patronages differed from those listed elsewhere.
For example, some patronages listed for Prince Charles on his own website did not appear on the royal site, and the research identified about 20 discrepancies concerning roles he holds.
It also discovered about five similar discrepancies between the royal site and the Duchess of Cornwall’s website, and about 35 for Prince Andrew.
Some charities were listed on the official site as simply having "members of the royal family" as patrons.
Giving Evidence said it had asked Buckingham Palace for a full list of royal patronages in an easily usable format, such as a spreadsheet, but was told that this was not available.
In a statement about the research, Caroline Fiennes, director of Giving Evidence, said the information held by Buckingham Palace was "inconsistent and incomplete, and very confusing".
She said: "Given that patronages are a good proportion of the work of the royals, who are publicly funded, they should surely be clearer, and this is basic management information for their own work.
"Perhaps they don’t know which royal is patron of what, or they don’t want the public to know."
The research also found that it was extremely difficult to distinguish which of the royals’ patronages were actually for UK-registered charities rather than other types of bodies such as military organisations, non-departmental public bodies and private members' clubs.
Prince Andrew, for example, is the patron of about 25 private members' golf clubs and at least two private members' yacht clubs, on top of his charity patronages, researchers found.
Fiennes said: "We are still unable to isolate the UK-registered charity patronages despite having now spent at least four person-weeks on it.
"For example, the Prince of Wales’s website lists him as patron of 'The Reserve Forces Ulysses Trust', whereas the royal.uk site lists him as patron of 'Ulysses Trust'. We think that these are the same thing, but cannot know, and the royals between them have hundreds of such patronages, which would need cross-checking."
She said this meant the figures quoted in the national press about the number of charities for which the royals were patrons were "almost certainly wrong".
Buckingham Palace was unable to provide a comment before publication of this story.