To take up their seats, they would have had to swear an oath - "I swear by Almighty God that I will be faithful and bear true allegiance to Her Majesty Queen Elizabeth, her heirs and successors, according to law. So help me God."
So if the Irish republicans had sworn an oath of allegiance to the queen, her heirs and their successors, they could have had the benefits of UK press freedom. Ok.
It's clear that the ban on Sinn Féin members speaking on television was an abuse (by the government). But given that the BBC sidestepped the ban by having them re-voiced by actors (purportedly making Thatcher furious) it's difficult to see them as anything other than independent-minded in this instance.
So if the Irish republicans had sworn an oath of allegiance to the queen, her heirs and their successors, they could have had the benefits of UK press freedom. Ok.