Recover - Sorry if I didn`t make myself clear.
When you are in the en-route or holding phase of a flight above the Transition Altitude, ie in the London TMA above 6000ft, then you should inform the controller if your rate of climb or descent during a level change either is or will be less than 500fpm.
This is not a prohibition on such rates of climb or descent which may be necessary for other reasons.
When you have been cleared to descend from a flight level to an altitude, then on passing through the Transition Altitude the obligation to inform ATC of a rate of descent which will be or is less than 500fpm ceases.
This is in order to allow you to comply with the Continuous Descent Approach Procedure.
Hope this is better.
Regards DoB