Soundly beat second-rate English political party (8)

I believe the answer is:

belabour

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'soundly beat' is the definition.
'belabour' can be an answer for 'beat' (I've seen this before). I am unsure of the 'soundly' bit.

'second-rate english political party' is the wordplay.
'second rate' becomes 'b'.
'english' becomes 'E' (abbreviation).
'political party' becomes 'labour' (I've seen this before).
'b'+'e'+'labour'='BELABOUR'

Can you help me to learn more?

(Other definitions for belabour that I've seen before include "Harangue" , "discuss at length" , "Beat" , "hit" , "Criticise harshly" .)

I've seen this clue in The Telegraph.

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