The RSGB has agreed with Ofcom an NoV to authorise the temporary use of the Regional Secondary Locator R after the United Kingdom callsign prefix.
The RSGB has announced today that UK radio amateurs wishing to celebrate the royal wedding can apply for a Notice of Variation to do so.
For further information see RSGB latest news
http://rsgb.org/main/blog/news/gb2rs/headlines/2018/05/04/special-callsign-letter-for-royal-wedding/
or
Apply for the NOV here
http://rsgb.org/main/operating/licensing-novs-visitors/online-nov-application/royal-wedding-rsl-nov/