GRAPHIC-Downgrades, profit warnings ring Brexit alarms for UK mid-caps

* FTSE 250 vs FTSE 100: http://reut.rs/2eCvwk9

* Profit warnings spark broker downgrades

* Earnings disappointments lead to outsized moves

* Senior, Cobham, Laird among midcaps warning on profits

By Kit Rees

LONDON, Oct 25 (Reuters) - A spate of profit warnings amongmid-sized British companies, big slides in stock prices and arush of broker downgrades have seen the third-quarter earningsseason off to a weak start as Brexit-related cracks start toshow.

So far profit warnings from smartphone maker Laird,engineers Keller and Senior, aerospace anddefence firm Cobham as well as a disappointing updatefrom NCC have triggered punishing share price falls.

A rally in the UK mid-cap index, which recoveredsharply from a slump following the referendum vote to leave theEuropean Union, has stalled over the past week as profitwarnings took their toll.

It is once again lagging the more internationally focusedFTSE 100, as this chart http://reut.rs/2eCvwk9 shows.

While the FTSE 100 is up around 11 percent since the June 23close, the FTSE 250 is up only 2.6 percent, having slipped froman all-time high reached earlier this month, at least in partbecause its constituents tend to be more exposed to a domesticeconomy whose growth could be constrained by Brexit.

By contrast, the greater international spread of FTSE 100members means their sterling profits and dividend-payingabilities actually benefit from the pound's multi-year weakness.

The outsized moves on stocks that disappoint illustrate howunforgiving investors are of weakness in company earnings.

Chipmaker Laird for example saw nearly half its market valuewiped off in a single day last week after warning of sharplylower profit, blaming a slowdown in smartphone sales and pricingpressure.

WORST DAY

Cyber security firm NCC Group also marked its worst dayever, tanking more than 35 percent after troubles with contractcancellations.

Senior fell 13 percent after blaming lower demand for partsused in heavy truck production for its profit warning, whileCobham lost a similar amount after its second profit warningthis year.

Brokers have scrambled to cut earnings expectations andprice targets on a slew of UK mid-range companies.

Laird, Countrywide, Howden Joinery Group,Mitchells & Butlers and Aldermore, all sawnegative broker activity on Tuesday, sending their shares 2.6percent to 5 percent lower on the day.

Almost every brokerage cited concerns about a post-Brexiteconomic slowdown impacting these businesses.

"Within the midcap area we've had a number of profitswarnings recently," Stephen Bailey, a fund manager onLiontrust's Macro-Thematic team, said. "A lot of those arestemming from either currency fluctuations or indeed theuncertainty that's been created by the Brexit vote.

"The economy stalled ahead of the Brexit vote ... and incertain areas it hasn't really got going again," Bailey added. "So it's not surprising we're seeing a number of these warningscoming through, and I would expect that's probably going to beset to continue." (Editing by David Holmes)