SLEEPY lawyers and bankers, exhausted after working on the takeover battle for AT&T Wireless, almost cost Cingular, the winning bidder, an extra $1.6 billion (£847 million) because of a clerical slip-up.

Cingular was forced to file a new acquisition agreement with the US Securities and Exchange Commission last night because the costly error had not been noticed and was therefore legally binding.

In the original final draft of the sale agreement, sealed on Monday night after Vodafone was forced out of the bidding, Cingular would have been forced to pay as much as $1.6 billion to AT&T Wireless if the takeover was not complete by December 16.

The “late fee”, based on an interest payment of 4 per cent of the $41 billion sale price, would have come on top of a $1.4 billion break fee if the deal were to fall apart.

There was much confusion among Cingular’s advisers in New York last night. At first they said that the interest payment was part of the deal, but was unlikely to be invoked because they expected it to clear all regulatory hurdles ahead of the December 16 deadline.

After some reflection, however, they changed their minds, saying that the interest payment, while apparently in the sale agreement, had actually been removed before the deal was signed. But within minutes, they changed their minds again when it emerged that the error had not been removed.

A senior City source tried to explain: “Look these guys haven’t slept for four days.”