RSGB Contest Special Rules 2018

S7.
This contest runs concurrently with all or part of an IARU co-ordinated contest. UK&CD entrants are encouraged to submit their log for the coordinated IARU contest here

On 4m and 6m MGM modes may also be used (except in CW only contests) provided the entrant meets the requirements of the IARU rules, see section 4.5 (MGM Contest operating procedures) on page 54 at http://www.iaru-r1.org/index.php/downloads/Documents/VHF/VHF-Managers-Handbook-V8.01/
You can find the RSGB guidelines on the use of MGM here