Old scheme by a UK politician is informative (11)

I believe the answer is:

explanatory

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'is informative' is the definition.
(similar in meaning)

'old scheme by a uk politician' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'scheme' becomes 'plan' (synonyms).
'by' becomes 'at'.
'a uk politician' becomes 'ory' (I can't justify this - if you can you should believe this answer much more).
'ex'+'plan'+'at'+'ory'='EXPLANATORY'

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(Other definitions for explanatory that I've seen before include "Clarifying" , "Serving to make something clear" , "illustrative" .)

I've seen this clue in The Irish Times.

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