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* FTSE 100 down 0.3 pct, mid caps up 0.2 pct
* Next, Randgold jump after results; Cobham leads mid caps
* Convatec slumps after earnings disappoint, CEO leaves
* Energy stocks, banks weigh
LONDON, Aug 3 (Reuters) - Earnings drove the action on Britain's FTSE 100 on Thursday, though strong gains in retailer Next and miner Randgold Resources were not enough to offset weakness in banks, energy stocks and medical technology firm Convatec.
The blue-chip index was down 0.2 percent at 7,394.82 points by 0853 GMT, in line with a broader decline among European indexes and ahead of a Bank of England policy meeting which is expected to see interest rates left on hold.
Shares in retailer Next were the standout performers, surging around 8 percent after it returned to sales growth in the second quarter, helped by warm weather and an improvement in its online offering.
"There's been concerns about the instore sales and are Next going to be able to shift towards consumer patterns -- (we're) starting to see more of an online presence as well in the Directory," said Jonathan Roy, advisory investment manager at Charles Hanover Investments.
"The reaction we're seeing today is more of a sigh of relief from investors because Next have consistently disappointed the market with results over the last couple of years."
Precious metals miner Randgold Resources also enjoyed gains, with its shares rising more than 3 percent after reporting a jump in first half profit and raising its production forecast.
But disappointing earnings weighed on shares in Convatec , which slumped more than 8 percent after posting a lower profit for the first half and also announcing the departure of its CEO.
Falls among cyclical stocks were the biggest drag on the blue chips, with energy stocks BP and Royal Dutch Shell tracking oil prices lower, while financials HSBC and Standard Chartered also added pressure.
Standard Chartered extended losses from the previous session after its results were overshadowed by the absence of a dividend.
"Standard Chartered's 2Q17 results confirmed our expectation that the company's recovery will take time ... with income growth still the key issue," Barclays analysts said in a note.
"Although we hadn't anticipated dividends being restarted before FY17, there was some expectation in the market that this could happen at Q2."
Outside the blue chips, Britain's FTSE 250 gained 0.2 percent, with beaten-down defence stock Cobham leading the charge, up 6.8 percent after its first half results showed the tentative signs of recovery.
"We remain convinced Cobham will respond well to a firm hand on the tiller and -- above all -- to mid-single digit demand growth in key end-markets like Defence," analysts at Jefferies said in a note. (Reporting by Kit Rees; Editing by Catherine Evans)