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* FTSE 100 closes 0.15 pct lower
* Aggreko biggest mid-cap faller after earnings miss
* Intertek top of FTSE on results surprise
* Standard Life falls back after merger excitement
* Ashtead drops on negative currency impact
* Weak pound supports shares
By Helen Reid
LONDON, March 7 (Reuters) - Britain's top equity index steadied at the close on Tuesday, with negative share moves seen by a string of firms following their poor earnings updates offsetting gains in some firms that advanced on the back of a weaker pound.
The blue-chip FTSE 100 closed 0.15 percent lower after trading in a narrow band throughout the session.
Gambling firm Paddy Power Betfair was the top FTSE faller, down 5.9 percent after it posted 2016 earnings up 35 percent and predicted 2017 would be in line with expectations. Analysts said the shares were fully valued.
"A business case founded on regulated earnings, complementary brands, marketing firepower etc. has its attractions," Liberum analysts said.
"However, on more than 20 times price-to-earnings, the valuation is 'rich' and operational challenges in gaming are still evident."
Ashtead was down 2 percent after the company announced its results and said that sterling fluctuations may continue to impact its performance.
Shares in the industrial equipment maker had gained 35 percent since the U.S. election on hopes of an infrastructure spending spree.
Fund manager Standard Life was also among the top fallers, down 3.8 percent, snapping a five-day winning streak after excitement over its plans to merge with Aberdeen Asset Management.
Insurer Direct Line was down 2.9 percent after its results were slightly dented by the government's decision last week to cut the discount rate with which personal injury claims are calculated. The company said the change should have little material impact on 2017 profits.
Temporary power provider Aggreko slumped 12.9 percent, the top mid-cap faller, after it said it expected lower profit this year and posted a 3 percent decline in full-year revenue due to low oil prices and adverse currency impact.
The company, whose largest utility business is in Argentina, said the impact of pricing discount to its contracts there would outweigh growth across the group.
"The update on Argentina is relatively disappointing," Morgan Stanley analysts said.
A lack of conviction on the stock could have accentuated the market reaction. Aggreko was one of the most-shorted stocks posting earnings this week, with 9 percent of its shares outstanding on loan, according to Markit data.
Product testing firm Intertek hit a five-month high, up 4.8 percent at the top of the blue-chip index, after its results beat on margins.
"The good surprise on the EBITA margin and on the cash flow have not been priced in," UBS analysts said.
Sterling fell to a seven-week low against the dollar ahead of a second vote in Britain's upper house of parliament on legislation giving Prime Minister Theresa May the right to start formal Brexit talks.
A weaker pound boosts performance in the FTSE 100, which has a majority of foreign currency earning companies.
Foreign exchange is having the greatest influence on UK stocks in 20 years, Morgan Stanley found. The bank sees a brighter outlook for sterling, spurring it to upgrade its view on British mid-cap companies. (Additional reporting by Atul Prakash,; Editing by Susan Thomas and Ed Osmond)