Britain's FTSE retreats from one-month peak, mid-cap index snaps winning streak

* FTSE 100 down 0.3 pct

* Energy, auto shares fall

* Ex-divs weigh

* Cobham slumps after results

* FTSE 250 snaps 7-day winning streak

By Kit Rees and Helen Reid

LONDON, Feb 16 (Reuters) - Britain's top share indexretreated from a one-month high on Thursday, weighed down by afall among oil firms and those trading ex-dividend, whilemid-cap engineer Cobham slumped after results.

The blue-chip FTSE 100 index ended the day down 0.4percent at 7,273.95 points, in line with a broader decline amongEuropean indexes. The FTSE dropped 28.46 points, of which 27.64were due to ex-divs, according to Reuters calculations.

A number of heavyweight companies dropped after tradingwithout entitlement to their latest dividend payout. AstraZeneca, BP, Royal Dutch Shell and ImperialBrands all fell between 1.2 percent to 3.4 percent.

Oil & gas and auto & parts stockswere the biggest weights on the index. Shares in Anglo American and Antofagasta fell 2 to 2.2 percent as theprice of copper eased.

The mid-cap index snapped its seven-day winningstreak, closing down 0.7 percent and off Wednesday's recordhigh, due to dramatic results-driven moves. Engineering firmCobham closed down 15.1 percent to seal its second-worstever day, after yet another profit warning.

Cobham took a 150 million pound sterling charge on atroubled contract with Boeing, leading it to downgrade its 2016profit target.

Drax Group also fell, down 5.3 percent afterreporting a disappointing set of results, with its core annualearnings falling 17 percent on weaker power prices and the lossof revenue from a green energy scheme.

However, a profit beat propelled Lancashire Holding's shares 8.7 percent. The property and casualty insurerposted a better-than-expected 2016 profit, helped by lowerexpenses and higher gains in the final quarter.

Challenger banks were also top mid-cap gainers after aPanmure Gordon note initiated rating on a handful of thelenders, which use new technology to erode traditional banks'customer base.

OneSavings Bank, Shawbrook and Aldermore were up 1.8 to 3 percent after Panmure analysts gavethem a "buy" rating.

"As large UK banks focus on cost reduction and commoditisedprice sensitive mainstream lending, the specialist lenders arefilling the gap in those lending markets which require greatersophistication and bespoke service," said analysts in a note.

On the small-cap index, Laura Ashley sharessank 10.7 percent to post their worst day in nearly six years,after the fashion and homeware retailer warned its full-yearprofit would miss targets.

The shares were through 16 times their average 30-day volumeby market close. (Editing by Jeremy Gaunt and Angus MacSwan)