The most recent statistics from the Law Society of Britain are as of 31 July 2008. The Society tallied 139,666 solicitors on its rolls. The number of those with practicing certificates was less, at 112,433.
The number of solicitors employed outside of private practice grew considerably, to 29,104. That does not mean that 29,000 British solicitors work in corporate legal departments, I believe, since many might not be practicing law. But at least we have another data point in the sporadic quest for the number of legal departments worldwide (See my post of April 13, 2006: estimates in the UK of 14.5% inside solicitors; and Feb. 8, 2010: UK had approximately 130,000 lawyers; Commerce & Industry has 11,000 members.).