Sort of door sadly unproved to secure area (2-3-4)

I believe the answer is:

up-and-over

'sort of door' is the definition.
(up-and-over is a type of door)

'sadly unproved to secure area' is the wordplay.
'sadly' is an anagram indicator.
'to secure' indicates putting letters inside.
'area' becomes 'a' (maths abbreviation).
'unproved' is an anagram of 'upndover'.
'upndover' enclosing 'a' is 'UP-AND-OVER'.

(Another definition for up-and-over that I've seen is " (Of door) rising into horizontal position".)

I've seen this clue in The Times.

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