I've notices that the tyres on the Mehari are are pretty badly split/cracked. They're all Michelin 125s with plenty of tread but some of the cracks, when theyre at the bottom of the tyre are big enough to put my little finger in

How old are they, Sam?

Old age even but dont even have to be that old!

Not sure Neil, I know one is newly fitted to the car, but was second hand... it's possible that they may be the originals.

Any post-80s tyres have the age marked on them. You're looking for three or four digits in a sort of oval, probably near the "DOT" marking.

If it's three digits, it's WWY - week number, year. If there's just the digits, they're '80s, if there's a triangle, they're '90s.
If there's four digits, it's WWYY - week number, year in the 2000s.

I had some, from new, that after about three years had a crackle-glaze type effect all around the sidewalls. Where the tread meets the side wall I suppose. Very fine cracks about 5mm long all the way around. They still had tread left and I don't know if they'd have made it dangerous, but I ditched them and thought why bother spending that much again! Toyos for me!

Depending on where you got 'em from, "new" might have been kicking around in storage for years...

A well known 2cv parts supplier. Dunno. I just wasn't impressed.

If the DOT code is less than 5 years ago then there's nothing to stop you sending them back to Michelin for a warranty claim. Any tyre is guaranteed to last 5 years or as long as the tread lasts, whichever comes sooner.

Any link for that...?