Unless you have permission, you may only feature members of the Royal Family in pretty limited circumstances, whether in TV advertising (which is covered by the BCAP Code) or adverting and marketing in any other media (which will usually be covered by the CAP Code).
When there's a royal event or occasion such as a royal anniversary, birthday or new baby on the scene, it may be possible to make various references, provided you do so without creating the impression of patronage or endorsement by the Royal Family.
However, you must not feature the Royal Arms or emblems in advertising/marketing materials.
On 20 November 2017, Queen Elizabeth II and Prince Phillip celebrate their 70th wedding anniversary, with the Royal Mint creating a commemorative platinum coin to mark the occasion. In other royal news, Prince William and the Duchess of Cambridge recently announced that they are expecting their third child, due in 2018. While marketers may be tempted to link their ad campaigns to these occasions, they should be mindful of the rules. See CAP's website for an overview of the main ‘dos’ and ‘don’ts’ when referring to the Royal Family in ads.