After Effects is exporting vector file animation pixelated

Did you tried making your logo like a Shape in a shape layer into After Effects? I thing you can do that with the Pen Tool because your logo is not very difficult to illustrate.

For colour I turned Image P3 on in project settings and colours seems to be matching better also

So it turns out the video size was just too small, Ive scaled up on the same ratio to 2100 x 675 and it is much better quality

Sure, there are better codecs than H264 but it depends what is the destination for this video. If you want a high quality codec then use Animation, Prores 422HQ, Prores4444 or Uncompressed in a Quicktime file. But this format will not be suitable for, for example, web or mobile device playback.

Also, you can do a couple of things before exporting. The first one is configuring your AE project to 16bpc (you can change this in the bottom of the project window). Also, you can check the Use Maximum Render Quality option in Adobe Media Encoder, located in the bottom right of your AME interface.

VBR is a more efficient profile encoding than CBR but sometimes can create some artifacts (degradation) when the analysis for the 2 passes establishes that there are no movement in the image. CBR maintains a constant bitrate for every single frame.

I have just recreated everything as shape layers and in an older version of AE to see if that's it but the video is still pixelated. I think it's happening in the export maybe. The colours are fading too, which I can't have happening as brand colours for the logo obviously need to be the same

Continuously Rasterize, read jenkmeister answer.

Do you have continually rasterize for the layer turned on? That Sun looking icon in the layer between shy guy and the quality setting. If not, try turning that on. That should ensure the vector file renders cleanly.