So no person is allowed to travel in a trailed unit (the law) which has recommended tyre replacement every 5 years but people can travel in cars with very old tyres that may have internal etc. issues due to age.
Both approaches/perspectives make an interesting debating point.
As far as I'm concerned there's no debate once you get age cracking it's going in the bin.
Had the cracks join up and nearly had a delamination on a Punto, tread was coming away from the carcass on the inner edge. Only discovered this the day after I'd been doing 95mph on a private test track. I'd taken the wheels off to check the brakes not look the tyres did what I was doing picked a wheel up and had a "Holy ****!" moment.
Since then I've been very careful as to what I have on the car. Not worth saving what works at out pence a mile to maybe have a massive accident.