The London Stock Exchange has blamed a technical issue with its Infolect data dissemination feed for the system failure that prevented some firms from trading yesterday afternoon (7 November).
Some traders were unable to complete trades yesterday even though the the exchange extended trading by more than an hour.
The company said there had been a "technical issue" with the Infolect system that caused some firms to lose connectivity, but emphasised that the Tradelect trading platform had "remained operational".
The Tradelect system went live in June after a four-year project and was upgraded last month to increase its capacity by 70% and speed by 40% in readiness for the London Stock Exchange's integration with Borsa Italiana.
"The cause of the technical issue has been identified and a solution implemented," a spokesman said, but declined to give any further details.
Bob Mc Dowall, a senior TowerGroup analyst, speculated that unusual and inexplicable "spikes" revealed in recent research into data transmission systems was the most likely cause of the problem.
"With the drive to lower and lower latency in data systems with huge volumes of data coming through in a short space of time, you are going to get these issues as you approach the boundaries of physics," he said.