The London trader who sparked a severe slump on the FTSE-100 Index on Monday evening keyed in a wrong figure, it was confirmed yesterday.

The London Stock Exchange (LSE) said its own inquiries backed earlier speculation that a trader's "sell" order was inadvertently too high.

An extra zero is thought to have turned a transaction for £30 million sterling (€48.6 million) into £300 million and sent the Footsie sliding by around 140 points. Those losses were recovered yesterday, although the LSE said it now wanted to investigate the computer safety checks at the firm involved.

City trading floors buzzed yesterday with speculation about the identity of the investment bank at the centre of the controversy.

US firm Lehman Brothers has been linked to the incident but has declined to comment.