All of the London "regulars" - 21/27/24 etc always use Alpha/Echo - without fail.
Very rare to use the Zulu lowest priority suffix - as when they are returning from a job if stood down (or positioning in the morning) then it is fairly high priority to get back on line for ops - so still some priority.
Normally Helimed 27 at Denham flies in to the Royal London Hospital as Echo but has been known to change to Alpha en route as they are tasked - but they need to get the Doctor on board.
The police helicopters on theother hand rarely use the priority suffix - as they are almost always Cat B - and is a waste of RT time. They advise us if NOT Cat B. I have seen them use the Zulu suffix when on a crew training/engineering flight.