Have breakfast, as all the king's horses and men did (2,2,4,2,2,3)
I believe the answer is:
go to work on an egg
'have breakfast' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'as all the king's horses and men did' is the wordplay.
I cannot quite see how this works, but
'as' could be 'eg' (I've seen this in other clues) and 'eg' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
'men' could be 'or' (military abbreviation for Other Ranks) and 'or' is present in the answer.
'king' could be 'k' (abbreviation for king in chess) and 'k' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for go to work on an egg that I've seen before include "classic advertising slogan" , "Former ovoid marketing slogan" , "What Faberge often did" .)