The London Stock Exchange tonight delayed a major update of its computer system amid concern that one of its key trading platforms had been targeted by a saboteur.

The Financial Services Authority has been informed of the exchange's suspicions and it is understood that the police have also been called in to investigate a shutdown which began at 8.23am today.

The LSE's Turquoise trading platform – used by hedge funds and high-frequency professional traders – remained shut until 10.30am, prompting a major internal investigation.

By tonight, the LSE admitted the problem may have been caused deliberately. A spokeswoman said: "Preliminary investigations indicate that this human error may have occurred in suspicious circumstances. The LSE takes this matter very seriously and a full internal investigation has now begun. The relevant authorities have been informed."

The problems at Turquoise, known in the City as a "dark pool" which allows participants to trade anonymously with each another, had major repercussions for the LSE which had been planning to transfer its entire share trading business, known as the main market, to a new system today.

The LSE had been under pressure from its customers to delay the introduction of the new computer system to allow further network upgrades even before the latest problems but has now been forced to abandon any updates until next year.

"The LSE will work in partnership with customers to agree a date as early and practicably as possible in 2011 to reschedule the main market migration," the exchange said.

The systems delays will be an embarrassment to the LSE's chief executive Xavier Rolet who bought the Sri Lankan company MillenniumIT last year to allow the exchange to overhaul its current technology systems so it can compete with the alternative trading platforms which have been springing up and posing a threat to the LSE.

The explosion of rival trading platforms has meant that trading in the biggest stocks in London has been drifting away from the LSE, which is now accounts of around 60% of trading in shares in FTSE 100 companies. By moving to the technology provided by MillenniumIT, the LSE was hoping to be able to offer the fastest trading platform in the world.

The transfer of Turquoise onto the new technology last month had already caused problems for the exchange, after it suffered glitches on its first day.