The NCT (or MoT) was only introduced in the Republic of Ireland in 2000 or thereabouts. Before that, you would see every kind of sh1tbox you can imagine on public roads in Northern Ireland, the drivers having crossed the border. This used to drive the RUC nuts, because the only recourse if you stopped a genuinely dangerous car, was either to issue a fixed penalty ticket, which you knew would never be paid, or arrest the driver/owner and throw them in police cells to appear in the Magistrate's Court the next week day morning. Which would create a lot of paperwork, for what everyone else would consider a relatively minor offence. This was at the height of The Troubles.
If the driver failed the attitude test. In other words, was gobby to the police on the scene, there was one other recourse. A suitably qualified officer was empowered to dismantle a car, at the roadside, where he reasonably suspected that multiple faults existed. There was no obligation for police to reassemble the car afterwards.
This could be done by a Constable on his own authority. I heard of it being done. By guys that I worked with. But I only witnessed it once. In the interests of brevity, I'll skip the details. Suffice to say, the driver thoroughly deserved it and photographs of his face, taken as he watched his car being dismantled, which we hung on the briefing room wall, made us smile every time we assembled to start a shift.