* FTSE 100 down 0.3 pct at close, mid-caps down 0.6 pct
* IWG plummets 32 pct on profit warning
* Warning on covenant breaches sends Interserve down 27 pct
* Acacia Mining soars after resolving Tanzania dispute (Updates with prices at close, adds detail)
By Helen Reid
LONDON, Oct 19 (Reuters) - Britain’s main share index fell 0.3 percent on Thursday as a weak third-quarter update from Unilever weighed, while mid- and small-cap trading was marred by profit warnings from IWG and Interserve which slashed their market value by a third.
Disappointing retail sales figures sent sterling to a one-week low before recovering, helping the internationally-exposed FTSE reduce earlier losses slightly.
Fresh from a record close, the FTSE 250 ended 0.6 percent lower as workspace group IWG plummeted 32.2 percent after warning on profit. It cited natural disasters and weakness in London trading as contributing factors.
The firm said it now expected its profits to be 160 to 170 million pounds, against their previous estimate of 216 million, sending shares to a 22-month low.
“There has been a strong sales uplift in October, but only time will tell if this converts to revenue performance,” Stifel analysts wrote in a note. “Caution is warranted.”
Although mid-caps have hit fresh highs, investor sentiment has softened into third-quarter results, with analysts revising down their expectations for earnings.
Investors have grown cautious around UK equities since Britain voted to leave the European Union in June 2016, sending the pound plunging and sparking uncertainty around the path of divorce talks.
Britain’s FTSE 100 has gained 5.3 percent this year against a 7.7 percent gain for the broader pan-European STOXX 600 index.
“I‘m not surprised that UK companies that derive the majority of their revenues from within the UK are starting to miss earnings forecasts,” said Christopher Peel, chief investment officer at Tavistock Wealth.
“The UK has become a relatively unattractive country to be invested in (bonds and equities) compared to continental Europe, Asia and the U.S.,” he said. British companies were likely to underperform global counterparts for the foreseeable future as a result, he added.
A 16.2 percent jump in battered Acacia Mining was a bright spot, however, after shareholder Barrick Gold reached an agreement with the Tanzanian government over an export ban.
On the FTSE 100, Unilever weighed, falling 5.5 percent after the consumer goods giant’s third-quarter results missed consensus expectations.
Unilever blamed poorer weather in Europe for slower than expected sales this summer, particularly impacting ice cream sales.
Support services and construction firm Interserve sank 27.2 percent on the small-cap index following a warning that it may breach covenants after a further deterioration in trading.
The group warned profits would be weaker than it had expected in September, suggesting profit in the second half would be half that of last year, Stifel analysts wrote, putting their target price and forecasts for the stock under review.
Carillion, which also provides support services to the construction industry, had plummeted earlier this summer after a string of profit warnings.
“We have plenty of support services firms that are doing OK, so I do think it’s specific to the companies like Carillion and the markets they serve, rather than an issue for support services in general,” said Colin McLean, director at SVM Asset Management.
Reporting by Helen Reid and Kit Rees, editing by Pritha Sarkar