Fail to keep appointment with last of mandarins in Whitehall etc (5-3)

'whitehall etc' is the definition.
(Jack Whitehall is a stand-up comedian)

'fail to keep appointment with last of mandarins' is the wordplay.
'fail to keep appointment' becomes 'stand-up' (as in standing someone up on a date).
'with' is a charade indicator (letters next to each other).
'last of' suggests the final letters.
The last letter of 'mandarins' is 's'.
'standup'+'s'='STAND-UPS'

'in' is the link.