Building in city to secure housing plan that’s had backing (5,5)

I believe the answer is:
tower block
'building' is the definition.
(I've seen this before)
'city to secure housing plan that's had backing' is the wordplay.
I cannot quite see how this works, but
'to' is within the answer.
'secure' could be 'lock' (locking is a kind of securing) and 'lock' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for tower block that I've seen before include "large building" , "Tall residential or office building" , "urban building" , "big build-up?" , "high-rise building" .)
