Establish bridge team in city in the past (8)
I believe the answer is:
Here is my best explanation:
'establish' is the definition.
'bridge team in city in the past' is the wordplay.
'bridge team' becomes 'ns' (north and south are a team in bridge).
'in' means one lot of letters goes inside another.
'city' becomes 'ec' (the City of London postcode).
'in the past' becomes 'once' (I've seen this before).
'ns' going into 'ec' is 'ensc'.