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* FTSE 100 up 0.4 pct, mid caps down 0.1 pct
* Carillion warns on profits, CEO quits
* Financials, energy stocks rise
* Miners among biggest fallers
LONDON, July 10 (Reuters) - Britain's top share index held firm on Monday as a rise among financials and energy stocks lent support, though a plunge in Carillion's shares after a profit warning weighed on mid-caps.
The blue chip FTSE 100 index was up 0.4 percent at 7,377.92 points by 0848 GMT, whereas the mid caps were down 0.1 percent, held back by a 32 percent fall in Carillion's shares.
The construction and support services group plunged nearly 40 percent after its CEO stepped down as it issued a full-year profit warning, citing difficult markets and deterioration in some contracts.
Carillion is one of the most-shorted UK firms, according to FCA disclosure data.
"(Carillion's) issued a profit warning, saying that profits are going to be lower ... also they've got a big debt pile, which isn't getting any smaller, and that all raises the prospect that they might have to raise more capital, perhaps through a rights issue at some stage," said Laith Khalaf, senior analyst at Hargreaves Lansdown.
"Put all these things together, add on top of that the CEO stepping down and you've got a pretty grisly statement and consequently a very negative reaction from the market."
Peer Balfour Beatty also fell almost 5 percent.
While moves among blue chips were fairly muted, financials added the most points to the index, with lenders HSBC and Standard Chartered making gains.
A firmer energy sector also helped lift the FTSE, with heavyweights Royal Dutch Shell and BP both up around 0.3 percent.
Precious metals miner Fresnillo was the biggest laggard, down 1.1 percent as the price of gold dropped to its lowest level in nearly four months, while peer Randgold Resources was also down 0.2 percent.
Basic resources firms Rio Tinto, Anglo American and Glencore helped bring up the rear, down between 0.7 percent to 1.1 percent on the back of a weaker copper price. (Reporting by Kit Rees; Editing by Keith Weir)