Well - somebody used the UK election as an excuse to dump SGH by the looks. Cameron plans to strip 700mGBPs or so out of legal aid for defending criminal actions. That isn't really Slater and Gordon's area of work anyway - so who cares!
Games being played - I suspect somebody's position was liquidated and contingent orders went off - there was crazy and un-neccessary selling at below 580 even - so other people's money issue by the look.