Exact same thing just happened to me this weekend, car just stopped with no warning! I'm going to try and claim through my finance company claiming a breach of my consumer rights but i'm not hopeful. Looking online it seems the problem is endemic!
i would say its a case for the ombudsmen and certainly run it past citizens advice to get some more guidance on pursuing a claim
If unsuccesful then a secondhand engine (with the revised cooling system parts) may be the most financially advisable way forwards