Thank you for the quick response.
On early testing that does seem to have fixed it. Although interestingly in one test to create a Bluray compliant mp4 the aspect ratio in TMPGEnc Authoring came up as 64:45 and so would therefore need re-rendering. However in Mediainfo it was correct, so quite strange. As a matter of interest a VP9 file was correct in Mediainfo and TMPGEnc (of course only for the aspect ratio of 16x9).
So I will need to do further testing on Bluray MP4's.
Thanks again