From a recent post by Bruce MacEwen’s in Adam Smith, Esq.
Finally, let us never underestimate the yin and the yang of the high degree of leverage on law firms’ P&L’s. That is to say, once you’ve covered your costs (which are, for the record, people @ ~60%, occupancy @ ~30%, and “everything else” @ ~10%), then essentially every additional dollar of revenue drops directly to the bottom line.
Also, if the average law firm’s gross margin is, say, 35%, then–if you do nothing to change your cost base–a 17.5% drop in revenue (highly plausible in this environment) implies a 50% drop in profits.
Add to that the highly liquid market for lateral partners and you have the ingredients for immediate and severe problems.
OK, it is not quite the same in the UK (clearly US firms work on a somewhat higher margin) but close enough.