Crossword Genius

Telegraph backing perjuror means it may be going downhill! (5,7)

Ross

I believe the answer is:

cable railway

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'it may be going downhill' is the definition.
The definition suggests a singular noun which matches the answer.

'telegraph backing perjuror means' is the wordplay.
'telegraph' becomes 'cable' (synonyms).
'backing' is a reversal indicator.
'perjuror' becomes 'liar' (I've seen this before).
'means' becomes 'way' (a way or means of doing something).
'liar' backwards is 'rail'.
'cable'+'rail'+'way'='CABLE-RAILWAY'

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I've seen this clue in The Telegraph.
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