Politician on the right road turned up decay (3,3)
I believe the answer is:
dry rot
'decay' is the definition.
(I have seen 'Decay of timber ' mean 'dry rot' so perhaps 'decay' could also mean 'dry rot')
'politician on the right road turned up' is the wordplay.
'politician' becomes 'tory' (term for a Conservative Party politician).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'the right road' becomes 'rd' (abbreviation. I am not sure about the 'right' bit.).
'turned up' says the letters should be written in reverse.
'tory'+'rd'='toryrd'
'toryrd' backwards is 'DRY-ROT'.
Can you help me to learn more?
(Other definitions for dry rot that I've seen before include "Decay of timber caused by fungus" , "Usual, customary" , "Degeneration" , "housing problem?" , "it may make one's beam disappear" .)