Another update after a bit of experimenting.
On the days that my car runs sluggish and feels like it's lagging, it retains that feeling for the whole of whatever journey I'm making - my daily trip to work is about 30 mins; even at the end of the journey the car feels like it hasn't warmed up properly if that makes sense? Whilst the revs at idle remain steady on such days, the engine sound still has a constant tremor / flutter - nothing majorly excessive but it's not there on the days when the car is fine.
Now the past couple of days I have been letting my car idle (warm up) for quite a while before I set off (I know that tecnically this is not great for cars). Anyway after it has been left for a while the engine sounds a lot smoother and the tremor / flutter seems to go. From the moment of then pulling away the car feels lighter and more responsive throughout the journey - the sound of the turbo spooling is also a lot more audible and consistent each time it starts to kick in. Generally the car feels much smoother, quieter and throttle response is much better and more sensitive.
Any more thoughts people? Something that my car always does EVERY morning when accelerating in 2nd (at 2.5krpm) from COLD, is hesitate once - I've been told that this is a generic fault of the LCR's ECU...so does everyone else have this? My car also has the old style coolant sensor (i/e not the green one) and I'm wondering whether to replace this.....?