| Thanks for the responses guys
The feel is not so much of a 'lag' its more of a lumpy acceleration on WOT (almost like your waiting for something to unblock itself before it becomes smooth again if you get what I mean!) In all fairness its not as bad as I make it sound, but I'm just not 100% convinced the performance is EXACTLY as smooth as it should be!
I do tend to do LOTS of short journeys like 1-2 miles per journey up to 5/6 times a day and only a few longer journeys at the weekend sometimes. I have also not been using anything other than regular unleaded, so i'm sure these 2 things contribute to the issue.
I think I'm gonna fill up with V Power and put some fuel system cleaner etc in (when I have decided what) and see how that goes. Might take out the air filter and check for crap as I'm not sure if BMW do this during the TLC services? Failing that some new plugs might be in order but we'll see how she goes. | 
