By Holly Williams, PA Business Editor & Lawrence Matheson Troubled water supplier Thames Water has hit a funding snag, with shareholders pulling the plug on a £500million investment plan. The company – which serves 15 million homes in London and the South East – said the funding plan, agreed last July, was subject to conditions, including a business plan that is supported by “appropriate regulatory arrangements”. But Thames Water said the regulations being imposed by industry watchdog Ofwat “make the PR24 plan “uninvestible”, and as a result the shareholder support letter from last July “has n…