Had a quick look in MATS pt1,However I cannot actualy find anything about holding R/T proc's for pilots.
Although it may annoy LTMA controllers I would strongly suggest that pilots report entering the hold.
i) not everybody involved in a holding stack has radar available to them.
ii) It is a good "nudge" for the ATCO when an a/c reports XXX entering hold at FL80.It informs the ATCO which levels remain ready to use.
Remember we are not allowed to use radar for seperation in the hold ,it has got to be procedural.
FiM