I don't know and I don't much care. Minimum billables are a poor indicator of how much work you will do. My group's hours are roughly comparable to US groups in the other City firms. I probably bill a bit more because I get "borrowed" by a British partner who does a lot of CIS work and he keeps very long hours. I love working with him, though, so I don't mind.
About how many hours of work = 1 billable hour (roughly)?