The London Stock Exchange has put the brakes on its cash markets migration to a Linux-based system after human error in “suspicious circumstances” floored the network on its Turquoise alternative trading venue.

Turquoise, a dark pool or anonymous trading platform, uses the same system, and this morning took trading offline for two hours after a “network issue”.

“Human error” was to blame for this morning’s outage on Turquoise, the LSE told the markets in a statement. But it added that the problem “may have occurred in suspicious circumstances”.

“The London Stock Exchange Group take this matter very seriously and a full internal investigation has now begun,” it said. “The relevant authorities have been informed.” It is understood the Financial Services Authority is already looking into the incident.

The system was due to go live on cash markets yesterday, but was last week postponed following tests until 15 November. It will now not go live until next year, because the LSE previously agreed with markets that it would freeze technological change in December.

“In light of this incident, coupled with necessary network upgrades to address ultra low latency and high flow inherent in the new platform, the Group has regrettably been forced to postpone its Main Market LSE technology migration for SETS [the main order book],” the LSE said.

The platform is billed as the fastest in the world.

The exchange said it “will work in partnership with customers to agree a date as early and practicably as possible in 2011 to reschedule the Main Market migration”.