See this article
If you are appealing against an ESA decision you are entitled to receive ESA while you wait for your appeal date IF you properly register a fit note from your GP at the same time as lodging the appeal.
BUT (a) this fact is being kept very very quiet and (b) GPs are being sent misleading letters as a matter of course during the critical time frame telling them NOT to issue any further fit notes, with no mention that a fit note will be needed if the case goes to appeal.
This doesn't affect me at all but I know plenty of mumsnetters will need this info.