Cockney's extremely vigorous when holding up flight, ultimately making you the last to arrive (8)
I believe the answer is:
tardiest
'the last to arrive' is the definition.
(tardy can mean late)
'cockney's extremely vigorous when holding up flight ultimately' is the wordplay.
I cannot really understand how this works, but
'when' could be 'e' (I've seen this in other clues) and 'e' is located in the answer.
'up' could be 'is' (I've seen this in other clues) and 'is' is found within the remaining letters.
This may be the basis of clue (or it may be nonsense).
'making you' is the link.
Can you help me to learn more?
(Another definition for tardiest that I've seen is " Striated in latest manner".)