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Trading on the London Stock Exchange has resumed after a technical malfunction closed it for all of Friday morning.

The bourse stopped automated trading for over four hours until 1215 GMT to investigate a "market data" issue.

The problem had been identified during Friday's opening auction, which is used to determine the day's starting prices on the exchange.

Stocks rose strongly when it reopened, catching up with European markets.

The FTSE 100 index ended the day 81 points, or 1.4%, higher at 6,001.

The rebound came despite downwardly revised UK economic growth data being released during the morning outage.

Investors were instead responding to growing confidence that Saudi Arabia would step in to secure global oil supplies, although many were left frustrated that they missed out on the brisk morning trading seen on other European indexes.

"We sincerely regret the inconvenience that today's disruption to trading has caused our customers," said LSE chief executive Xavier Rolet.

The exchange decided not to extend its trading hours to make up for the lost trading time.

An LSE spokesperson added that orders-driven securities trading - which comprises the bulk of trading on the exchange - had resumed.

Quote-driven trading continued throughout the day but this form of trading is very small in comparison with orders-driven trading.

The exchange earlier noted that it had "moved its main market trading to the MillenniumIT system earlier this month", but did not specify whether this lay behind the error.

Trading on the Borsa Italiana - which is owned by the LSE - was halted for three and a half hours on Tuesday, also because of a computer error.

According to the exchange, that incident was unrelated to Friday's London suspension, and the two exchanges use different technology platforms.

"In this day and age, you simply cannot afford not to have your technology in duplication," said David Buik of brokerage BGC Partners, speaking on Bloomberg television, criticising the exchange's apparent lack of a back-up system.

"If it's not foolproof, where is the alternative?" he said.

And City Index market strategist, Joshua Raymond, added: "At a time of uncertainty in the markets, where traders are having to keep on their toes with the situation in Libya, the last thing they need is an unexpected halt to trading."