On-going support mainly blocking means of access (2,8)

I believe the answer is:

in progress

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'on-going' is the definition.
Both the answer and definition are adjectives.
Maybe there's an association between them I don't understand?

'support mainly blocking means of access' is the wordplay.
'support mainly' becomes 'pro' (I am not sure about this - if you are sure you should believe this answer much more).
'blocking' indicates putting letters inside (to block can mean to plug a gap in something).
'means of access' becomes 'ingress' (I've seen this in another clue).
'pro' inserted into 'ingress' is 'IN PROGRESS'.

Can you help me to learn more?

(Other definitions for in progress that I've seen before include "Under way" , "still going on" .)

I've seen this clue in The Guardian.

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