The 10% of chips which, according to Sarson's, don't get their vinegar are likely to be sharpened with the 'non-brewed condiment' almost universal in northern chip shops. This is not a cheap substitute but an ethanoic acid solution just like traditional vinegar, made by a process which does not begin with beer, and which gained popularity with the Temperance Movements of the early 20th Century.
The leading providers, Drywhite Ltd, also supply it in a concentrated form called 'Maltflaven', to be diluted for use.