Flipping Ulster PM's come round too late (5,2)
I believe the answer is:
sleep in
'come round too late' is the definition.
(sleep in can mean to wake up late)
'flipping ulster pm's' is the wordplay.
'flipping' says the letters should be written in reverse.
'ulster' becomes 'NI' (Northern Ireland).
'pm's' becomes 'Peel's' (19th-century prime minister Robert Peel).
'ni'+'peels'='nipeels'
'nipeels' in reverse letter order is 'SLEEP IN'.
(Other definitions for sleep in that I've seen before include "Stay late in bed" , "Wake later than intended" , "Get up late" .)