Comp sci at bad uni or chemical engineering at Good uni

First off, what do you want to study? These are pretty different degrees.

really and truly its computer science but I believe I can go to a better uni than this. I have achieved AAB and the B is in chemistry. Therefore I could have the chance of redoing chemistry and hopefully getting A/A* and going to a better uni than Kent. My dream would be Kings or UCL for comp sci.

But at the same time, I could do my Bsc in Kent and do a masters in computer science at Kings or UCL so im not really sure.

really and truly its computer science but I believe I can go to a better uni than this. I have achieved AAB and the B is in chemistry. Therefore I could have the chance of redoing chemistry and hopefully getting A/A* and going to a better uni than Kent. My dream would be Kings or UCL for comp sci.

But at the same time, I could do my Bsc in Kent and do a masters in computer science at Kings or UCL so im not really sure.

Then would you be happy to take a gap year? If what you want to do is CompSci I'd do that - why even consider ChemEng?
AAB are good grades and I'm sure you would be capable - CompSci is very employable though so it may matter less what uni you go to, especially if Kent has industry links. But if you want to take a gap year and aim higher, that is also valid.

I was literally in your shoes 5 years ago. Missed my firm offer at Imperial/UCL by an A grade. Went through Clearing and got offered Chemical Engineering at Uni of Edinburgh and Chemistry at Uni of Manchester. I wanted to do ChemEng but preferred Manchester as the uni (more reputable in my opinion, and 3 years in England vs 4 in Scotland). I ended up taking a gap year instead to retake exams, retaking Chemistry and Maths for a final 3As as opposed to ABB. Applied to UCL again for ChemEng and got in again. I didn't even end up going and instead took my scholarship to go to uni in the States (which I also applied to during the gap year).

All in all, follow what you most want to do and believe in. If you really want CompSci, then go to Kent, get a first or 2:1 and aim for a Master's at Imperial/UCL/King's after. But make sure you get a 2:1 minimum. If you think you can do better now, take the gap year and apply again. Chances are you'll improve your grade. Don't do ChemEng just because Southampton sounds better, because when you get there you might be in a bigger pickle if/when you get there and realize you wanted CompSci all along.

Not sure what all this fuss about KCL for CS is, they're a pretty average (perhaps even mediocre) CS department; not comparable to UCL and neither are even close to comparable to Imperial...