Old man or woman heretic securing Irishman as MP? (15)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

PARENT (old man or woman) + ARIAN (heretic) containing [securing] LIAM (Irishman). Of course parents don’t have to be old, but here we have a reference to the somewhat disrespectful way that offspring sometimes refer to their mother or father as ‘the old man / woman’.