KKR and TPG Capital, two of the largest US private equity groups, are facing a battle to secure shareholder approval for their $45bn buy-out of TXU after one of the Texas-based energy group’s largest investors said it opposed the deal.

Franklin Resources, a mutual fund company based near San Francisco, disclosed a 5 per cent stake in TXU in a regulatory filing and said the planned take-over at $69.25 per share was “significantly below TXU’s current actual value”.