OK, so thanks everyone who replied and the suggestions. I've done a ton of research and have decided to save around £250-£300 by not going for the obvious GoPro choice. I have gone for this:
http://www.veho-muvi...product/k2npng/
I will hopefully have it up and running for my first track day next Saturday and I will post up the video produced to let you all see the quality, or not, of the pictures. I decided that I did not need 4k capability (I don't have a 4k TV and so 1080 quality on the monitor / tablet will be fine and it comes with a huge range of extras and a hard case. It does seem like a bargain, but the reviews are good and it uses the GoPro mounts too so the range of options is huge.
Cheers, and thanks again.