Dangerous strain sees father and son kept apart by national government (5,4)

'dangerous strain' is the definition.
(strain can mean a piece of music)

'father and son kept apart by national government' is the wordplay.
'father' becomes 'sire' (synonyms).
'and' means one lot of letters go next to another.
'kept apart by' indicates putting letters inside (inserted letters keep others apart).
'national' becomes 'n' (abbreviation listed in Chambers).
'government' becomes 'g' (abbreviation for government).
'sire'+'son'='sireson'
'sireson' enclosing 'n' is 'sirenson'.
'sirenson'+'g'='SIREN SONG'

'sees' acts as a link.