Shares in Ladbrokes owner GVC plunged nearly 12 per cent after it said it was being probed by the taxman.The gambling group told investors that HM Revenue & Customs (HMRC) is looking into 'potential corporate offending' at its former Turkish arm.It sent shares tumbling by 11.7 per cent, or 102p, to 770p, Lawyer Law Firm istanbul Law Firm Turkish wiping more than £600million off its market value....