Interserve Share News (IRV)

* FTSE 100 down 0.4 pct at close

* Indivior tumbles 6 pct after patent litigation loss

* GSK up after exits Pfizer consumer health bid

* Asia-exposed funds tumble(Updates prices at close)

By Helen Reid

LONDON, March 23 (Reuters) - Mounting fears of a globaltrade war after the U.S. slapped tariffs on imports from Chinasent British stocks to a 15-month low on Friday.

The FTSE 100 ended the session 0.4 percent lower at6,921.94 points, clawing back some losses after hitting itslowest level since December 2016 in early trading.

Investor unease extended to the response from China, whichurged the United States to "pull back from the brink", andunveiled its own plans to impose tariffs on up to $3 billion ofU.S. imports.

Bank stocks and miners were the biggest drags as risksentiment soured and the most trade-sensitive sectors suffered.

Some felt this was a long-overdue selloff in stock markets,which enjoyed an unusually robust 2017 but have run intoobstacles since the start of last month.

"It could have been anything that caused it, it justhappened to be trade," said Daniel Lockyer, senior fund managerat Hawksmoor Investment Management.

"The market is a discounting mechanism and we didn't thinkit was discounting enough risks out there, whether it'scorporate earnings disappointing, political risks, the end ofQE," he added.

Indivior shares plummeted more than 20 percent atthe open before recovering, ending down 6.3 percent, after thepharma firm lost a patent protection case, setting it up forcheap competition to its opioid addiction treatment.

A U.S. court ruled generic drugs firm Alvogen had notinfringed three of the British firm's patents, a blow toIndivior whose Suboxone Film treatment accounts for as much as80 percent of its revenue.

GSK rose 3.3 percent after it pulled out of thebidding war for Pfizer's consumer health business afterReckitt Benckiser did likewise earlier this week.

Smiths Group dropped 4.4 percent to the bottom ofthe FTSE 100 after reporting a weaker first-half profit thanexpected. The engineering group pointed to currency headwindsand higher R&D costs.

Next bounced 7.7 percent to the top of the indexafter its annual results, with investors relieved the clothingretailer did not issue a profit warning.

A broadly challenging retail environment has caused many ofBritain's high street stores to suffer sharp losses, making Nexta relative winner.

UK-listed funds invested in Japan and China were among theworst performers on the mid- and small-cap indexes after a routin Asian trading overnight.

Baillie Gifford Japan Trust fell 2 percent, whileFidelity China Special Situations tumbled 3.1 percent.Among small-caps Fidelity Japanese Value shares dropped3.4 percent and Schroder Japan Growth Fund lost 1.4percent.

(Reporting by Helen Reid and Kit ReesEditing by Andrew Heavens and John Stonestreet)