Smell of rotten eggs from engine

I've noticed today that when I start my car I get a smell of rotton eggs. The car passed the NCT is August so I'm presuming the catalytic converter would have passed muster??

Could it be anything else as I am sick at the thought of having to fork out for a new Cat.


Thanks

I thought that a rotten egg smell is common/normal on cars with a cat??

Some cars are more prone that others, wind direction also a factor, what model and age is the car...?