Stanley Gibbons shares lost more than a quarter of their value after the stamp dealer blamed weak trading in Asia and difficulty completing sales of high-value items for its second profit warning in six months.

In an unscheduled trading update, the dealer in rare stamps and other collectibles said first-half profit and margins would be well below the same period last year, when it sold plenty of profitable sought-after items.

Revenue and profit should pick up in the second half of the year that ends in March but the company would not hit annual forecasts, it said. The outlook is a reversal on guidance issued two weeks ago when Stanley Gibbons said it expected to hit profit forecasts.

The company said: “On the basis of the performance in the first half, the board now believes that, as a result of the weakness being experienced in our Asian operations and the continued illiquidity in high-value stock items, it is unlikely that the group will achieve the market forecast for the full year.”

The shares, down by almost two-thirds this year, fell 27% to 104p.

Stanley Gibbons’ house broker, Peel Hunt, halved its estimate for annual pre-tax profit to £5m from £10m. It said there was a great deal of uncertainty about the result, which depended on the timing and size of sales of high-value items.

The 159-year-old company warned in April that several big sales had not completed by the end of the last financial year but said it expected them to go through in the first half of the current year. Recent trading was affected by the delayed sale of a large collection of stamps and coins.

Trading has been difficult since the first half of last year when it sold an Edward VIII coin for a record £516,000. Business then was boosted by people in China buying stamps and coins but the country’s economy has been hit by slowing growth and a stock market crash.

The Peel Hunt analysts said the company had also been distracted by a management shakeout after the acquisitions of Mallett Antiques and other businesses.

“The departure of a number of senior executives should resolve these issues, which should enable management to refocus on delivering sales and profits. This has combined with a weaker market in Asia which has impacted demand,” the analysts said.