* FTSE 100 down 0.8 pct, biggest daily fall in 6 weeks
* Index extends losses after weak U.S. data
* Pearson suffers biggest daily fall in 12 years after update
By Francesco Canepa
LONDON, Jan 23 (Reuters) - Britain's main equity index suffered its biggest one-day fall this year on Thursday, weighed down by disappointing U.S. economic data and weak updates from Easyjet and Pearson.
Global stocks extended losses in the afternoon as data showed U.S. manufacturing growth slowed in January for the first time in three months. The data further undermined sentiment towards the world's largest economy after discouraging earnings reports from bellwether companies such as McDonald's Corp .
The FTSE 100 closed 53.05 points lower, or 0.8 percent, at 6,773.28 points, a third consecutive daily fall and the biggest since Dec. 12.
The index is still up roughly 5 percent since mid-December, boosted by flows of money into Europe on the back of better-than-expected data in Britain and the euro zone, which are responsible for half the sales generated by UK blue chips.
"We are holding our longs at the moment as we feel the UK markets are looking stronger than the U.S.," said Ed Woolfitt, the head of trading at Galvan.
British shares trade at a 16 percent discount to their U.S. counterparts based on their respective price-to-earnings ratios, the steepest valuation difference in seven years, Datastream data showed.
The FTSE, which hit an 8-months high on Tuesday, fell in just eight of the last 24 trading days. Each dip was followed by a stronger bounce over the following few days. Some traders bet this time will be no different.
"All the little moves (down) ended up being bought, so it's likely that it will be the same case here, albeit this one is a bit more dramatic," Giles Watts, head of equities at City Index, said.
Watts still expected the FTSE to head towards the record high of 6,950 it set in late 1999.
Shares in Pearson plunged 8.2 percent, their biggest fall in 12 years, after the publisher reported big restructuring charges alongside weak demand in its education businesses in North America and Britain.
"There are a lot of structural pressures on the business and we don't see any sort of mitigation of these pressures near-term," said Investec analyst Steve Liechti, who put his estimates, price target and recommendation for the stock under review after the update.
Easyjet was also among the top fallers, off 4.1 percent after the budget airline indicated that first-half seasonal losses would be higher this year than last year because Easter falls in its fiscal second half.
"At the minute people are just trying to get out. Some of the longer-term players are taking profits (on Easyjet)," said Vinay Sharma, trader at Gekko Global Markets.
Basic materials knocked 2.9 points off the FTSE as data showed activity in China's factory sector contracted in January for the first time in six months, according to the Markit/HSBC PMI, pointing to a weak start in 2014.
Robert Quinn, the chief European equity strategist at S&P Capital IQ, said he preferred continental European indexes to the FTSE in light of the latter's larger weighting in basic materials, energy and consumer staples stocks. All of those sectors are expected to suffer from an ongoing economic slowdown in emerging markets.