High crimes at last with Conservatives' lies (4,7)

'lies' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'high crimes at last with conservatives'' is the wordplay.
'high' becomes 'tall' (associated in meaning).
'at last' indicates one should take the final letters.
'with' means one lot of letters go next to another.
'conservatives'' becomes 'tories'' (informal term for the Conservative Party).
The last letter of 'crimes' is 's'.
'tall'+'s'+'tories'='TALL STORIES'

Can you help me to learn more?