I don't know anything about the specifics of public advertising in the British newspaper market, but I will say that a substantial ad buy two days a week could

I don't know anything about the specifics of public advertising in the British newspaper market, but I will say that a substantial ad buy two days a week could be a significant subsidy to the paper as a whole. And how much you paid for the Saturday supplement is irrelevant: what matters is what the advertisers paid for that reprint.