Unknown individual in London band? (4)

I believe the answer is:

zone

I'm a little stuck... Click here to teach me more about this clue!

'london band?' is the definition.
'zone' can be an answer for 'band?' (thesaurus). I am not sure about the 'london' bit.

'unknown individual' is the wordplay.
'unknown' becomes 'z' (represents an unknown value in algebra).
'individual' becomes 'one' (an individual is one person).
'z'+'one'='ZONE'

'in' is the link.

Can you help me to learn more?

(Other definitions for zone that I've seen before include "Designated or defined area" , "Particular area or sector" , "District, area" , "Marked area" , "One of five belts round the earth" .)

I've seen this clue in The Independent.

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