Retention on the Active List was limited to 5 Star officers when they relinquished their 5 Star appointments ie they retired. Hence Admirals of the Fleet, Field Marshalls and Marshalls of the RAF all enjoyed 'retirement' on full pay. Very nice to!
The CDS held 5 Star rank until several years ago when that nice little earner status was regraded to 4 Star.
I believe the words at the time stated that 5 Star rank would only be re-instated during War-Time - whatever that may be defined as in todays big wide world.
lm