Trading was stopped yesterday from 3.04pm until the close as the exchange investigated "an issue impacting our trading and information platforms". The problem is understood to be connected to one of the exchange's servers.

The issue affected around one in 12 London instruments and closing prices were calculated using the last automatic trade executed or last bid and offer. For quote-driven stocks closing prices were calculated using the last best bid and offer.

By this morning, the LSE Web site was reporting that TradElect and Infolect were available as normal.

Customers were told to complete a full reference data download, purge all executed orders on impacted securities, confirm the deletion of all orders via an own order book download and resubmit all off-book trade reports for which an acknowledgement was not received.

Coming less than a month after the LSE suspended trading in a handful of stocks after a glitch in part of its market data feed, the latest problem will damage the bourse's reputation as it fights of competition from upstart rivals such as Chi-X, Bats and Turquoise.

To compound the embarrassment, the gremlins struck on the same day plans to increase hosting capacity fivefold were outlined.

Since taking charge of the exchange, new chief Xavier Rolet has made technology upgrades a priority. He has agreed to buy Sri Lanka's MillenniumIT for around £18 million and use the vendor's technology to replace TradElect.

MillenniumIT will become the LSE's in-house software development team, gradually replacing current suppliers and bringing its intellectual property to the company.

Rolet is also in exclusive negotiations with the bank-owned Turquoise platform on a deal that could see it merged with the LSE's Baikal dark pool.