My thought is that you need to familiarize yourself with the many media containers and codecs to which you can render your AE animations:
Sorry Dave, that does not help.
I looked through all of these FAQ's and similar problems on youtube before I asked here. I've re rendered it out in several formats but nothing seems to get below 3.9 G
I know which codec I need to use, for what I am using it for and I am completely aware of other codecs....
It seems to be an image problem, this is very odd as I've done countless other projects in a similar way and never had this problem.
If you use the AME and the YouTube preset you will get a compressed file. If your file is way bigger than you think it should be then either your composition is way bigger than you think it should be or you have changed some of the default settings, or the audio compression settings are not standard, or image you have chosen does not respond well to compression because of the detail and contrast of the image.
Thank you Rick, I've just downloaded AME, and I will try that.
Whilst I've been waiting for an answer I have been playing around with the Image file. I cut off a lot of the background and used a block colour. and blurred the rest of the image, then lowered the render quality by 1/4 this has cut the overall rendered file size from 4.02 G to just 600 MB and quality is still there ... so I'm happy with that.