Mirror covers Number Ten's first open policy (8)
I believe the answer is:
glasnost
'policy' is the definition.
(I know that glasnost is a type of social policy)
'mirror covers number ten's first' is the wordplay.
'mirror' becomes 'glass' (looking glass).
'covers' is an insertion indicator.
'number' becomes 'no' (abbreviation).
'ten's first' becomes 't' (1st letter of 'ten').
'glass' placed around 'no' is 'glasnos'.
'glasnos'+'t'='GLASNOST'
'open' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for glasnost that I've seen before include "Soviet policy of openness" , "Gorbachev initiative" , "Gorbachev's policy from 1985" , "Gorbachev's policy of "openness"" , "Policy of openness under Gorbachev" .)