Elderly person keeping heritage body readily available (2,3)
I believe the answer is:
on tap
'readily available' is the definition.
(I've seen this before)
'elderly person keeping heritage body' is the wordplay.
'elderly person' becomes 'OAP' (old-age pensioner).
'keeping' indicates putting letters inside (some letters kept inside).
'heritage body' becomes 'nt' (I can't justify this - if you can you should give a lot more credence to this answer).
'oap' placed around 'nt' is 'ON TAP'.
Can you help me to learn more?
(Other definitions for on tap that I've seen before include "Where to find a washer" , "Always available" , "kept in a cask" , "Of liquid gas, ready to be drawn off" , "readily accessible" .)