The RSGB has announced that Ofcom has kindly agreed that UK and Crown Dependency radio amateurs may use the “R” prefix in their callsigns during May and June 2023. A Notice of Variation (NoV) will be required and you can apply via the RSGB website.
See More https://rsgb.org/main/the-coronation-of-the-king-and-the-queen-consort/coronation-call-signs/