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 (Other OTC: CBHMF - news) slumps after results

* FTSE 250 snaps 7-day winning streak

By Kit Rees and Helen Reid

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

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

A number of heavyweight companies dropped after trading without entitlement to their latest dividend payout. AstraZeneca (Swiss: AZN.SW - news) , BP, Royal Dutch Shell (LSE: 0LN9.L - news) and Imperial Brands all fell between 1.2 percent to 3.4 percent.

Oil & gas and auto & parts stocks were the biggest weights on the index. Shares (Berlin: DI6.BE - news) in Anglo American (LSE: AAL.L - news) and Antofagasta (Other OTC: ANFGF - news) fell 2 to 2.2 percent as the price of copper eased.

The mid-cap index snapped its seven-day winning streak, closing down 0.7 percent and off Wednesday's record high, due to dramatic results-driven moves. Engineering firm Cobham closed down 15.1 percent to seal its second-worst ever day, after yet another profit warning.

Cobham took a 150 million pound sterling charge on a troubled contract with Boeing (NYSE: BA - news) , leading it to downgrade its 2016 profit target.

Drax Group (Frankfurt: D9F2.F - news) also fell, down 5.3 percent after reporting a disappointing set of results, with its core annual earnings falling 17 percent on weaker power prices and the loss of revenue from a green energy scheme.

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

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

OneSavings Bank (Stuttgart: 2OS.SG - news) , Shawbrook and Aldermore were up 1.8 to 3 percent after Panmure analysts gave them a "buy" rating.

"As large UK banks focus on cost reduction and commoditised price sensitive mainstream lending, the specialist lenders are filling the gap in those lending markets which require greater sophistication and bespoke service," said analysts in a note.

On the small-cap index, Laura Ashley (LSE: ALY.L - news) shares sank 10.7 percent to post their worst day in nearly six years, after the fashion and homeware retailer warned its full-year profit would miss targets.

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