A politician in the streets forming impressions (6)
I believe the answer is:
stamps
'impressions' is the definition.
(I know this)
'a politician in the streets' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'in the' indicates putting letters inside.
'streets' becomes 'sts' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'mp'='amp'
'amp' placed within 'sts' is 'STAMPS'.
'forming' is the link.
Can you help me to learn more?
(Other definitions for stamps that I've seen before include "Imprints" , "Brings foot down heavily onto the ground" , "Brings one's foot down heavily on the envelope" , "Cuts out with a die" , "Philatelists collect them" .)