Erskine May states the following:
The Crown is hereditary, subject, however, to special limitations by Parliament; and the King or Queen has always enjoyed, by prescription, custom and law, the chief place in Parliament and the sole executive power. The right of succession and the prerogatives of the Crown itself are, however, subject to limitations and change by legislative process with the consent and authority of the Sovereign; and in the exercise of the prerogatives and powers of the Crown the Sovereign now, by constitutional convention, depends on the advice of Ministers of the Crown, who continue to serve in that capacity only so long as they retain the confidence of Parliament.
What is considered to be "advice of Ministers of the Crown"? Is there a specific Minister or subset of Ministers to which this refers, or does it refer to the collective, perhaps through the passing of legislation to grant "permission" for the use of such powers?