Designate a duty current and order transportation (4,1,4)

I believe the answer is:

call a taxi

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'order transportation' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'designate a duty current' is the wordplay.
'designate' becomes 'call' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'duty' becomes 'tax' (I've seen this in another clue).
'current' becomes 'I' (physics symbol).
'call'+'a'+'tax'+'i'='CALL A TAXI'

'and' is the link.

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I've seen this clue in The Daily Express.

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