SERA does not include some of the previous UK rules of the air - the CAA still impose a number of exceptions to SERA and some additional rules have been retained. Part of your link says:
The result is that the UK has retained a small number of domestic Rules of the Air and issued a number of General Permissions and General Exemptions.
Unfortunately, the CAA website and its post-SERA info is as poor as its admin. The piece I quoted earlier is from this consolidation document, page 30, highlighted in yellow - which I think means it is UK Means of Compliance and Guidance Material. They don't make it easy.
https://www.caa.co.uk/WorkArea/Downl...?id=4294975756