Pipe been cut and plugged?

Hello all. 

I've noticed that for some reason a pipe has been cut and plugged and when running the pipe chucks out what smells like exhaust fumes which is going into the car.

I've only recently noticed this pipe thing and I can only assume it was done by mechanics when my heating wasn't working this January. 

Whatever they done sorted the heating but now I'm using the Aircon the smells have got really bad! 

I've tried to put up pics of rhe offending pipe in hope that someone will know whats going on.

Many thanks