In my 40 years on the road I have had 2 sets of tyres crack, the first were Continentals at 6 months old and the second were 4 year old Michelins with 5mm still remaining.

National tyres replaced the Contis but I had to pay up front new tyres. After a few weeks I got a cheque for the tread remaining, almost paid for the tyres, happy with outcome.

The Michelins were my summer tyres and since I only discovered the cracking when I swapped the winter tyres onto the car getting them replaced was not an emergency. Spoke to Michelin expecting them to tell me to go away but I was delighted when they said their tyres wer garanteed for 6 years against such issues. I got them removed form the rims by the friendly (and cheap) mobile tyre fitter up the street) and took them to ATS who returned them to Michelin, no cost to me. A few weeks later a cheque for £195 dropped through my door which bough a set of nice "mid range" tyres in the spring. Delighted with outcome.

So my advice is to contact Conti and see what they offer.

Even in the UK, 3mm is the recommended minimum because wet grip tails off very quickly below that.

There are moves to get the EU minimum increased from 1.6mm to 3.0mm but getting widespread agreement across the EU is a bureaucratic nightmare.