Almost sounds like the O2 sensor has things a little amiss! That's where I would start. How did you get the codes? If by a BMW mechanic, what were his suggestions? The heat sensors are a way of saying that the exhaust temperature is not right both before and after the cat. converter. Too rich or too lean a mixture caused by a faulty O2 sensor could create such a situation. As for the air bag light, that one is a mystery to me and should not be related to each other. However, things do go amiss in the ECU causing strange things. I had an air bag light come on when I was hammering off a rear brake rotor. The thing is the car was OFF when I was working on it. It triggered the mechanical sensor under the rear seat even though it had no electrical power to it when I was hammering on the stuck rotor! Get a good mechanic in the London area and have it looked at by a professional!
Good luck!