After watching the film all the way through the feedback is that the Big Ben sequence is too quick.
So have gone back and extended. Also made the DMP bigger to allow more 'movement' within it. In order to fake a small amount of parallax I added some foreground rocks.
The long shot is that this is too much for Motion to cope with once you add all the filters and live action footage of debris and dust. Think it's down to the pixel size of the main background. At the moment it won't render properly.
Therefore tonight I will render out the background with live action added and all the motion effects. Then open a new project and add the UI effects and filters and do a final render and see if that works okay. May need breaking down more but see how we go!
End titles down so just this sequence to resolve and it's all done.