Escalating trade aggression sends FTSE 100 spiraling

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* FTSE 100 down 1 pct

* Indivior tumbles 5 pct after patent litigation loss

* Smiths Group down 11 pct

* GSK pulls out of Pfizer consumer health bid

* Asia-exposed funds tumble

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 fresh 15-month low on Friday, erasingall the gains the UK's leading stock index made in 2017.

The FTSE 100 was down 1 percent by 0930 GMT, hittingits lowest level since December 2016 in early trading.

Investors warily eyed the response from China, which urgedthe United States to "pull back from the brink", and unveiledits own plans to impose tariffs on up to $3 billion of U.S.imports.

Bank stocks and miners were the biggest drags on the Britishmarket as risk sentiment soured and the most trade-sensitivesectors suffered.

Some felt this was a long-overdue sell-off in stock marketswhich 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, last trading down 6.5 percent, afterthe pharma 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.

"Whilst this is disappointing news, given there remainmultiple hurdles before a generic Suboxone film can launch inthe US, we still see the launch of a generic in 2018 asunlikely.

GSK rose 3 percent after it pulled out of thebidding war for Pfizer's consumer health business <PFE.N,>following in the footsteps of Reckitt Benckiser earlier thisweek.

Smiths Group sank 10.2 percent to the bottom of theFTSE 100 after reporting a weaker first-half profit thanexpected. Both profit and revenue fell short of analysts'expectations, with the engineering group pointing to currencyheadwinds and higher R&D costs.

"Delivering the now expected 8 percent organic growth and 70basis points year-on-year margin improvement in the second-halfis key to the investment case going forward, in our view,"analysts at Credit Suisse said.

Double-digit falls in share prices after results have becomea common feature of the UK stock market in the past months."There's little margin for error," said Hawksmoor's Lockyer.

Meanwhile Next jumped 4.6 percent to the top of theFTSE after its annual results, with investors relieved theclothing retailer 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 3.5 percent, whileFidelity China Special Situations tumbled 2.9 percent.Among small-caps Fidelity Japanese Value shares dropped4 percent and Schroder Japan Growth Fund lost 3.8percent.

(Reporting by Helen ReidEditing by Andrew Heavens)