By Tim Hanlon The head of theMetropolitan Police service has apologised to Stephen Lawrence’s mum for not fulfilling a promise to answer questions stemming from a BBC investigation into the murder of the 18-year-old. The broadcaster says Baroness Doreen Lawrence was promised an explanation after the BBC last year named Matthew White as the sixth suspect in the case. Despite initial correspondence with Deputy Assistant Commissioner Matt Ward, no update or explanation has been given. Metropolitan Police Commissioner Sir Mark Rowley has now issued an apology, saying: “On top of the failures over …