By Graham Hiscott Shareholders of Britain’s biggest water company are being accused of trying to blackmail the watchdog into agreeing bumper price hikes. Investors at crisis-hit Thames Water yesterday refused to stump-up a promised £500million, raising the possibility of the company being rescued by the taxpayer. The sorry saga has triggered concerns about the financial health of other suppliers, given the sector is carrying £57billion of debt. Thames, which owes £14.7bn, supplies one in four UK homes and has been slammed for its poor track record on pollution and service. The company’s nine s…