Deliveryman playing Portishead, not working hard (6)

I believe the answer is:

postie

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'deliveryman' is the definition.
(I know that postie is a type of deliveryman)

'portishead not working hard' is the wordplay.
'portishead' becomes 'p' (head letter of 'portis').
'not' becomes 'o' (I've seen this in other clues).
'working hard' becomes 'stie' (I can't explain this - if you can you should give a lot more credence to this answer).
'p'+'o'+'stie'='POSTIE'

'playing' is the link.
I am not very happy about this link. It may be part of another bit of the clue.

Can you help me to learn more?

(Another definition for postie that I've seen is " Mail deliverer (informal)".)

I've seen this clue in The Independent.

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