Re: Your Roots man, don't loose sight of your roots
I get the impression that this is "post pub" in the sense that it's the sort of thing you'd buy from a fast food / takeaway place while staggering home- a la doner kebab. They, of course, will have made large quantities of the sauce in advance.
You *could* make it yourself, but you probably wouldn't bother doing it as a one-off most of the time; certainly not when one was ratarsed, as you suggest.