How did Soros breake BoE?

Well, I know that Soros's hedge fund had been selling pounds for DM, but what the point of that? I mean, how can you make money playing like that? As far as I know, they sold 10 billion worth of pounds, it means they got 10 billion worth of DM. 1 pound was worht 2.7 DM and after devaluation, it went to, say, 2.3 DM for 1 pound. So how exactly in this case Soros made his money? Or the principle of the trade was different?