Make a special study of a former premier (5)

I believe the answer is:

major

I'm a little stuck... Click here to teach me more about this clue!

'study of a former premier' is the definition.
'major' can be an answer for 'study' (thesaurus). I'm not sure about the 'of a former premier' bit.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for major that I've seen before include "Leading - ex-Prime Minister" , "Pre-eminent" , "Big - PM" , "Important - ex-PM" , "John --, ex-PM" .)

I've seen this clue in the Evening Standard.

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