Peter puts up 20 homes for agents (4,6)

I believe the answer is:

safe houses

'homes for agents' is the definition.

'peter puts up' is the wordplay.
'peter' becomes 'safe' (slang term).
'puts up' becomes 'houses' ('house' can be a synonym of 'put up').
'safe'+'houses'='SAFE HOUSES'

'20' is the link.
This may not be correct. It may belong to another bit of the clue.

I've seen this clue in The Guardian.

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