new delhi/mumbai, Oct. 16 -- Yes Bank Ltd's bondholders scored a landmark win over India's central bank and the government on Thursday, with the Supreme Court striking down a six-year-old decision to cancel their investments. The Reserve Bank of India had seized the wobbly private lender in 2020 to facilitate a bailout, appointing an administrator who wrote off the bank's additional tier-1 (AT-1) bonds worth Rs.8,415 crore. The Bombay High Court quashed the write-off in 2023, and the apex court on Thursday said it found no reason to reverse that. "The question is not whether the AT-1 bonds could have been or ought to have been written down off. The question is the manner in which it was done," the judgment penned by justices Dipankar Datta and Augustine George Masih said. The administrator could not exercise a power reserved for the RBI, the court said, noting the write-down was contrary to the RBI's own master circular on Basel-III capital regulations and the terms governing the bonds. Yes Bank shares plunged 14.5% to Rs.18.12 on the NSE, turning the worst-performer in the Nifty Bank index, as investors fretted about the ruling's financial impact.The impact on Yes Bank's balance sheet may not be immediate. According to the former chief financial officer of a private sector bank, since AT-1 bonds do not have a maturity date, lenders only need to pay coupon every year. However, most AT-1 bonds have a call option under which banks repay investors in full after five or 10 years. Therefore, unless the verdict is overturned, Yes Bank will have to restart making yearly coupon payments to bondholders, the banker said on the condition of anonymity. The fate of the past dues-from 2020 to now- could not be immediately ascertained. The court made withering criticism of the central bank-"the RBI was a mere bystander, allowing the CET-1 ratio of Yes Bank to drop to an astonishing low of 0.6% while the business of Yes Bank was being carried out in a clandestine manner," the judgment said. The court added that making investors bear the consequences of administrative lapses is "highly unfair". The court was not persuaded that the write-down was necessary to revive Yes Bank before the State Bank of India (SBI) infused capital into the lender. It said the need to rescue the bank could not override procedure....