(In paragraph 11, corrects to clarify that Nomura is not M&S's joint house broker)
By James Davey
LONDON, March 20 Marks & Spencer, Britain's biggest clothing retailer, lost market share over the last three months, industry data showed on Thursday, reversing a small gain late last year that was heralded by its chief executive as a sign his recovery plan was working.
Data from research group Kantar Worldpanel, seen by Reuters, showed M&S's share of the UK fashion market declined 0.2 percent in the 24 weeks to Feb. 16 and was down 0.4 percent in the latter 12 weeks of the period.
The figures showed the retailer's share of the key womenswear market contracted 0.2 percent over the 24 weeks and 0.5 percent over the latter 12 weeks.
The loss of share is likely to up the pressure on CEO Marc Bolland, who has presided over 10 straight quarters of declining underlying sales in M&S's general merchandise division, which includes clothing.
Bolland is nearing the end of a three-year, 2.3 billion pound ($3.8 billion) plan to address decades of under-investment.
In January he said the womenswear business was showing "early signs of improvement" under the management of a new team and a re-focus on quality and style.
He highlighted womenswear market share growth of 0.1 percent over the 12 weeks to Nov. 24 - the first growth in three years - and said the firm's spring/summer collection had been well received by the fashion press.
M&S declined to comment on the latest market share data.
Shares in the firm were down 1.2 percent at 467 pence at 1254 GMT, valuing the business at 7.64 billion pounds.
The stock is down 7 percent over the last six months, though up 18.7 percent over the last year.
Earlier this week brokerage Nomura reduced its 2013-14 and 2014-15 pretax profit forecasts on concerns of continued weak trading at the retailer, which also sells upmarket food.
Its forecast for 2013-14 was cut to 614 million pounds from 632 million pounds - a forecast below sector analysts' consensus figure of 628 million pounds published on M&S's corporate website.
Nomura cut its forecast for 2014-15 to 709 million pounds from 724 million pounds.
The brokerage reduced its forecast for M&S's fourth-quarter like-for-like sales in general merchandise to down 1.5 percent from up 1.3 percent previously. It also cut its forecast for food like-for-like sales in its fourth quarter to flat from up 0.3 percent previously.
Easter - which normally boosts trade - falls later this year, while M&S's business will not have been helped by widespread flooding in Britain.
M&S is scheduled to update on fourth quarter, to end-March, trading on April 10 and publish 2013-14 results on May 20.
Separately on Thursday Next, Britain's No. 2 clothing retailer, posted a 12 percent rise in 2013-14 pretax profit to 695.2 million pounds - a figure that would top M&S's earnings for the first time, based on analysts' forecasts. ($1 = 0.6014 British Pounds) (Editing by David Holmes and Pravin Char)