* Concludes investigation into possible systems sabotage
* Delayed upgraded system now to go live on Feb. 14 * LSE plans dry runs on Jan. 29, Feb. 5
* Shares close up 5 percent
(Adds client comment, detail, background)
By Luke Jeffs
LONDON, Jan 11 (Reuters) - The London Stock Exchange said human error rather than sabotage caused a system crash last November, in a statement welcomed by some of its top clients who have long questioned the bourse's claim.
The LSE notified the police and launched an investigation when its Turquoise trading system buckled on Nov. 2, citing "suspicious circumstances" as it decided to delay a technology upgrade originally slated for mid-November.
"The investigation found the incident was the result of human error and the incident has now been closed," the exchange said on Tuesday. It gave no further detail.
The announcement came as no surprise to some of the British exchange's top investment bank clients, some of whom had expressed doubts about the likelihood of sabotage.
"I don't know why they raised the suspicion of sabotage in the first place, I can't see how they thought that would look better than the obvious explanation -- human error," said a managing director in trading at one large European investment bank, requesting anonymity.
Another managing director at a large trading firm said several firms had been calling for a delay to the migration of the main UK order book weeks before the glitch. "The LSE didn't even need to suggest sabotage when announcing the delay," this person said.
A spokesman for the LSE said it now planned to migrate its main British equity market to the new Millennium technology, intended to enable members to seal deals more quickly and in higher volumes, on Feb. 14, after dress rehearsals on Jan. 29 and Feb. 5.
Some of the exchange's largest trading members welcomed the new upgrade date, saying they had long completed their preparations for the planned changeover.
"We have done all our internal work to offer clients faster access to the main LSE market but the systems have been gathering dust since November," said one of the MDs.
The British exchange moved its smaller Turquoise system to Millennium in October as a dry run for the planned migration of its larger British order book Sets on Nov. 15.
The LSE wants to move its two main trading systems to Millennium IT, which it hopes will attract more business from high-frequency trading firms.
LSE shares closed up 5 percent. (Editing by Dan Lalor and David Holmes)