England captain once seen with son in nightspot (5)

I believe the answer is:

roost

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'england captain once seen' is the definition.
I can't tell whether this definition defines the answer.

'son in nightspot' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'in' is an insertion indicator.
'nightspot' becomes 'root' (I can't explain this - if you can you should believe this answer much more).
's' placed into 'root' is 'ROOST'.

'with' acts as a link.

Can you help me to learn more?

(Other definitions for roost that I've seen before include "where fliers land" , "It's sometimes ruled" , "Bird's night-time perch" , "Glowing with joy" , "Bird's night spot" .)

I've seen this clue in The Independent.

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