£9 would get you four loaves of bread[2] and three jars of peanut butter[3]. You'd have to be pretty hungry to eat enough of that for them to make a loss.
I assume the concept is fairly experimental at the moment, presumably they won't want people sprinting in, making an espresso for 3p and running out. Or I might have misunderstood what I read in [1]. In any case, it'll be interesting to see how it shakes out.
[1] http://now-here-this.timeout.com/2014/01/08/pay-per-minute-c... [2] https://www.ocado.com/webshop/product/Wholemeal-Bread-Medium... [3] https://www.ocado.com/webshop/product/Crunchy-Peanut-Butter-...