The decision to allow the Duke of Sussex to wear his uniform during a vigil at the Queen’s coffin was made by his father, King Charles III, royal sources have said.

Charles also requested that the Queen’s eight grandchildren be allowed to participate in the vigil – standing in quiet contemplation around their grandmother for 15 minutes as a mark of respect – something they were all keen to undertake.

Harry, who saw action on the front line during two tours of duty in Afghanistan, has been denied the chance to wear his military uniform, as he publicly mourns, because he is no longer a working royal.

Despite being a former Army officer, he has been in civilian dress for official events, including walking behind his grandmother’s coffin on Wednesday when it was carried to Westminster Hall for lying in state.

An exception had been made for the disgraced Duke of York, who is no longer a working royal but will wear his military uniform as a “special mark of respect” for the Queen when he stands guard around her coffin during a vigil with his siblings on Friday evening.

The royal source said the Prince of Wales will stand at the head and the Duke of Sussex at the foot. At the King’s request, they will both be in uniform. The other grandchildren will be in morning coat and dark formal dress with decorations.

William will be flanked by his cousins Zara Tindall and Peter Philips, while Harry will be with Princesses Beatrice and Eugenie, with Lady Louise and Viscount Severn at the centre of the coffin.

The source said the grandchildren, at the King’s invitation, were very keen to pay their respects – just as their parents are doing on Friday evening.