Vauxhall Zafira knocking sound from engine

My car started with a loud knocking sound today which I think was coming from inside the engine and the engine sounded like it was surging although I was stopped at a junction. I drove on for a few minutes but had to stop as i could smell burning, there was smoke in the engine but i couldn't tell whereabouts it was coming from. The breakdown guy came out and checked the car over and toosk it for a driv but it was fine apart from a small oil leak but the oil level was ok. I drove back home, about 7 miles, and the knocking started again, and when I pulled up it was really loud coming from the engine and smelt really strongly of burning. I had the cambelt replaced in January and a new clutch and dual mass flywheel in February. Does anyone have any ideas please