Sorry for cross-posting as I was meeting a project deadline and needed to solve the problem urgently.
Anyway these are the solutions offered to me;
If you render an interlaced output the amount of MB is effectively halved by the “doubled” frame rate of interlaced images, compared to the non-interlaced preview. Try increasing the shutter size in Comp Settings if you are unhappy with the amount of MB. – Andrew Yoole from Adobe Forums
You can change/adjust the motion blur settings in AE by going into the