Steeped grains plus malt extract:
Theakston's Old Peculier is a well known example of a British old ale or stock ale. This clone is based on a BYO recipe, with hop changes (Challenger and Target) and OG adjustment (1.055 estimated from 5.6% ABV) based on the official web site.
Source: Brew Your Own: Big Book of Clone Recipes (2018). Quarto Publishing Group, p. 171.