* FTSE 100 down 2.3%, FTSE 250 down 1.9%
* New threat from Trump on tariffs drives global falls
* Banks, miners, oil majors biggest drags
* RBS drops after warning on outlook
* British Airways owner IAG gains on profit beat (Updates shares, company news items)
By Muvija M and Shashwat Awasthi
Aug 2 (Reuters) - UK shares plunged to their lowest in a over a month on Friday after U.S. President Donald Trump threatened to hit China with more trade tariffs, while a Brexit-induced warning on targets knocked shares in Royal Bank of Scotland.
The FTSE 100 index .FTSE slumped 2.3% on its worst day fo far this year, while the FTSE 250 midcap index .FTMC weakened by 1.7%.
All of the major constituent sectors on both indexes ended with losses for the day.
Asia-focussed bank stocks, including HSBC HSBA.L , and oil majors Shell RDSa.L and BP BP.L led losses on the main index after Trump vowed to impose a 10% tariff on $300 billion worth of Chinese imports from Sept. 1.
Industrials Melrose MRON.L and Ashtead AHT.L , typically more exposed to global trade conditions, both lost about 5%.
RBS RBS.L plummeted 6.5% to a seven-month low as it warned that deteriorating economic conditions before Brexit were likely to derail next year's profitability and cost targets. Airways owner IAG ICAG.L , however, jumped 8.4% - its biggest one-day gain in eight years - after reporting strong profit numbers for the first half of its key summer period. WHIPLASH
The last major escalation of the U.S.-China trade tensions was behind a sharp drop in the FTSE 100 in May, but the index is still on course for its biggest annual rise since 2016 as Brexit-driven weakness in the pound helps the index's largely internationally-focused companies.
"Anyone trying to determine the next move in stock markets in the last 24 hours would be justified in feeling like they've just experienced a bit of whiplash," said CMC Markets analyst Michael Hewson.
"It is not hard to underestimate how much this abrupt escalation has caught markets unawares."
Miners .FTNMX1770 slumped nearly 4% to a two-month low as Chinese iron ore futures dropped after Brazil announced a rebound in exports of the steelmaking material in July. The index, which includes global players Glencore GLEN.L and Rio Tinto RIO.L , is on course for its steepest weekly fall since March.
The long-drawn out trade war has also weighed on the sector as China is the world's top metals consumer.
Among a handful of gainers on the midcap index was Britain's largest click and collect operator PayPoint PAYP.L , which jumped 7.2% after a deal with Deutsche Post's DHL Parcel UK as the latter looks to expand its click and collect services. firm Thomas Cook TCG.L surged 33%, a day after Nesat Kockar, the owner of Turkish tour operator Anex Tourism Group, disclosed a holding in the company. U.S.-China trade war roils global markets
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