Can the OP please change the title of this thread to remove the reference to Top Gear? The likelihood of the fault being down to the exhaust is very low indeed. I know, because I have one, and I have a lumpy idle that I'm pretty confident is down to a lazy lifter. There are any number of things it could be on the OP's car and when reading the thread title, people will infer the problem is caued by the exhaust, when it won't be, and Top Gear's good name will have been tarnished unfairly.
By all means change the title back once you've proven the fault lies with the TG exhaust and not your car.