Thames Water’s biggest investor has slashed the value of its stake in the company to zero in a move that renders the troubled supplier effectively worthless, The Telegraph can disclose. The Canadian pension fund Omers said it has been forced into a “full write down” of its investment in Thames, a day after withdrawing its representative from the utility company’s board. The write-down represents a complete loss for Omers, which valued its 31.7pc stake in Thames’ parent Kemble at £700m at the end of 2022. Newly filed documents for a Singapore-registered entity owned by Omers reveal the investment giant’s latest position on Thames, which is racing to avoid a taxpayer-backed bailout. The latest accounts show it had valued its stake in Thames’ parent Kemble at around £260m in December, which represented a 62.8pc fall over the last financial year. However, this has since fallen to zero after Omers joined other shareholders in cutting off funding from Thames, claiming it had been rendered “uninvestable”. This shortfall led to Kemble, Thames’ parent, defaulting on its debts earlier this year. Omers’ bosses said these events, which took place after its year-end in December, have led to “a full write-off of the investment”. This marks...