The Royal Veto has not been used since the reign of Queen Anne (The Scottish Militia Bill in 1708). It is effectively dead.
Constitutionally, the King or Queen is required to act on the advise of his or her ministers.
It is up to the voters to change the Crown’s ministers when they render bad advice.
Reserve powers do not require ministerial advice in every case. Not to mention, their non-use has to do with a “responsible government”, which the UK has of late not had nor was there in the 60s.
King Baudouin of Belgium refused assent on abortion laws in 1990; that was circumvented by the parliament there declaring him unable to rule, but for just one day.