The London Stock Exchange's top trading rivals failed to capitalize on the UK exchange's four-hour crash Friday as trading slowed across the market after the LSE's second trading glitch in a week.

Chi-X Europe's trading was down 20 percent at 1.6 billion euros ($2.21 billion) and Bats was off 21 percent on the daily average for the previous five days, at 600 million euros at the close of normal trading, Bats data shows.

The UK exchange's trading volume Friday was down 37 percent to 3.3 billion euros at the close, while the daily total for all UK platforms was a third lower at 6 billion euros.

The LSE blamed a technical glitch for the stoppage, which forced it to delay the start of trading until 1215 GMT (7:15 a.m. EST). The LSE-owned Borsa Italiana also experienced a glitch this week that delayed its opening to mid-afternoon Tuesday.

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

Chi-X Europe and Bats Europe, which are set to merge this year after an agreement last Friday, had three-quarters of UK orders in the morning when the LSE was down, compared with about 30 percent on a normal day.

But the total value of trading on the alternative trading platforms, known as multi-lateral trading facilities, was heavily down for the day, raising questions about the MTFs' reliance on the LSE as a reference point.

A spokeswoman for Chi-X Europe said: We provide strong competition in normal times, but volumes have been low today, which shows that not all firms are connected to Chi-X Europe yet, so there are more growth opportunities out there for us.

Mark Hemsley, chief executive of Bats Europe, said the nature of the LSE outage played a part in the slower than average trading through the rest of the day.

The opening is the worst possible time to crash because there is no reference price, but this situation was compounded by the fact that they accepted some orders but it was not clear if they were executed or not. If they had crashed during the day, we would've been well up, Hemsley said.

The exchange has been working hard in the past six months to update its trading systems to make them faster and better able to compete with Ch-X Europe and Bats Europe.

This latest glitch will further erode people's confidence in the new technology and the LSE's ability to manage the platform, Hemsley said.

MTFs have emerged over the past three years and won market share from Europe's largest exchanges by offering faster trading systems and lower fees.

But traders remain reluctant to trade in earnest when the primary exchange is not working, citing concerns over the reliability of the prices available on the MTFs.

(Editing by Will Waterman)

($1=.7233 Euro)