Marstons do the 'Simply' brews for Tesco whose IPA is very similar to Pedigree*, but with added citrusy, late-boil hops for aroma. But I'm not sure who does the Sainsburys house brand, though it'll almost certainly be one of the big boys.
*Aldi selling this for £1.25 a bottle at the moment. Hardly worth the effort of brewing my own at that price!