Overall its quite a simple fix. I found a small art brush buried in the bottom of my tool box which was similar diameter to that of an ink insert for a Bic Biro pen - DO NOT USE A SCREWDRIVER. Tape up the area with some masking tape to avoid any scratches to the paintwork, you can then lift the handle up two thirds of the way and look behind the top of the cover, you'll see two metal looking clips which are attached to each other in the shape of one long metal slider.
Click on pictures to enlarge slightly:
The slider/clip moves from left - right to open and the other way to close; I inserted the handle end of the thin art brush and pushed the slider to the open position. This made the handle really loose and you can then pull the top out a couple of millimetres which allows you to move the door handle cover downwards where you can disengage the bottom from two hooks.
Once the cover was off I just pinched the ends of the slider inwards a little to gain more purchase onto the handle cover and then re-assembled - you slide the clip right to left from the other side of the handle to secure the cover. Problem solved and all done in 5 minutes.
Job done, hope that helps.

Sam