The London Stock Exchange is examining dealings in Powerscreen shares late last week. Powerscreen shares fell 231/2 p to 110p sterling in London after the announcement; in Dublin, the shares dropped 62p to close at 129p.

A deal on Friday last involving the sale of 690,000 Powerscreen shares at 133p - a 20 per cent discount on the last dealt price - was notified to the exchange on Tuesday.

An exchange spokeswoman said that parties in large trades have up to five days to notify the exchange. But she added that all "unusual" share price movements are examined on a day-to-day basis "so automatically we would look at this deal".

Yesterday Guardian Royal Exchange, which sold most of its stake of just over 3 per cent in the group on Friday, categorically denied that it was involved in the 690,000 share deal. Declining to disclose the price at which it sold about 2.5 million shares, a spokesman said they were sold in one block and at a discount in order to sell a block of that size.

Stock market sources speculated yesterday that the 690,000 share deal involved short-selling by a Powerscreen "bear" - someone selling shares they did not own who would then buy shares when the price fell to fulfil their sale deal and make a profit on the trade. And, at the 110p closing price last night, the profit for a bear would have been £159,000 sterling.