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, wiping more than £600million off its market value. Probe: Ladbrokes owner GVC told...