The Independent Photographers Association work within the guidelines specified by the Buckingham Palace Press Office. These can be found on the British Monarchy Website:
"The Royal Rota is a system of allocating media positions at Royal engagements to ensure that as many media organisations as possible have access to Royal material without overcrowding a particular venue. Royal Rota material is provided on a reciprocal basis and must not be regarded as exclusive to the Rota pass holder. The Royal Rota party is a group of up to 20 photographers, cameramen and reporters chosen by various press organisations and representing all the media. They make their material available to local and national end users, as well as overseas media when appropriate.By means of the Rota, the press party is kept to an optimum size; this means that they do not get in the way of each other or of other guests, whilst ensuring that their material receives the widest possible distribution. Royal Rota material is in no way controlled or censored by Buckingham Palace Press Office, which is responsible only for seeing that adequate media facilities are given to the press to report public engagements undertaken by the Royal Family. The format and size of Royal Rotas are arranged in consultation with the host organisation, by Buckingham Palace or Clarence House Press Office".
Full details can be found using the following link.http://www.royal.gov.uk/LatestNewsandDiary/Mediaguidelines/TheRoyalRota.aspx