The offer includes Fullers' London Porter, which IMO has a higher flavour/ethanol ratio than Golden Pride. Sucrose added to the brew may improve keeping quality, but provides ethanol without useful flavour, so I'm always cynical about the virtues of high alcohol content of ale/porter per se.
OT, I suspect that Sainsbury's London Porter (brewed by Shepherd Neame) is closer to a proper 18th century porter than Fullers', though I've not tried brewing anything remotely like that.