The eventual problem was found by logging my car Vs another S3 and looking for differences
Cheers Alex, I think that logging it will be the only way to find out for sure now, probably the step I should've just started with to be honest..
Fuel filter been changed?
Also, how many cranks we talking? Try get a vid?
I had a pretty extensive service done last year of which changing the fuel filter should've been done as part of this? I will check the documentation when I get home tonight though to make sure.
I only have one video which isn't the best as I'm in a car park and there's a diesel with its engine running next to me but you can just make mine out after a couple of watches as you hear it struggling and see the rev needle stuttering prior to starting. I'll try and get a better one but it's so hard as its fine most of the time and only has difficulty sometimes, there's no clear pattern. I'll upload the video to Youtube and will link it to here after this post and as you'll see, it cranks over between 2-3 seconds before finally starting.
A random shot in the dark.
I had issues with starting on my 08 S3. Turns out the timing was slightly out. Alex at AKS found it when it went to be mapped. A pin in one of the pulleys had broke and caused the pulley to slip out of place a touch. Very relieved he found it and didn't cause any permanent damage (as far as I'm aware). Anyway since it was fixed the car starts without problem whether it's hot or cold.
Interesting to know, thanks for the information mate, I'll make sure to tell the guys at Storm absolutely everything I know.
Cheers for the help guys, appreciate it.