I have a Mondeo that won't start, I have had a suggestion that it might be a collapsed manifold cat......

symptoms are, really struggled to start, finally got it going, went a couple of miles and started chugging and struggling. Opened bonnet and some smoke coming up, running slightly hotter than normal. Oil and water as they should be. Hit/scraped the exhaust on a kerb the night before, hence the suggestion of the exhaust......

Any advice would be gratefully recieved