THE last of the great privatisations, AEA Technology, made a powerful stock market debut, but not even the enthusiasm generated by that story was sufficient to keep the FT-SE 100 index in positive ground.

The leading index ended a frustrating session marginally lower at 3,933.2, down 2.5 points, and never looked like consolidating Wednesday's strong gains. The latter followed the decision of the US Federal Reserve to hold interest rates steady against widespread predictions of an increase.

Second-line stocks were not really challenged, enabling the FT-SE Mid-250 to edge a net 1.8 ahead at 4,404.9.

Market-makers became increasingly edgy about London's performance as the day wore on, noting the emergence of more and more institutional sellers, albeit in small size.

"London is looking increasingly tired and reluctant to move higher. Unless there is a big boost to sentiment, I think we're going to move sideways or lower," was the view of one senior trader, who said the 4,000 level on Footsie was beginning to look further and further away.

There was also the widespread suspicion that, without any positive influences from Wall Street, London needs the impetus of at least one more big takeover to get Footsie moving back towards 4,000.

Turnover in equities was 633.6 million shares, while retail business on Wednesday was £1.6 billion sterling.