Strong performances from the FTSE 100's three mining stocks, following the proposed merger of Billiton with Australia's BHP, provided a much needed cushion for London's benchmark index on the eve of the third anniversary of the FTSE 100's first move through the 6,000 mark.

But not even the substantial gains in the miners, plus a handful of others, could prevent a late slide during the post-market auction, which saw the 100 index finish a net 11.2 down at 5,551.6.

The late dip concluded a difficult trading session which saw turnover come out at 1.7 billion shares, well down on most recent levels. Before the auction decline, Footsie had made a valiant attempt at a rally, with confirmation of the Billiton/BHP merger injecting a flurry of enthusiasm.

At its best, during the first hour of trading, the index pushed up 46.4, recrossing 5,600 as it did do. After that brief flourish the buyers quickly moved back to the sidelines, the index falling back to record a 26.4 fall at worst.

But the modest decline in the FTSE 100 could not disguise what was a generally uninspiring day in the broader market, where the FTSE 250, SmallCap and the Techmark 100 had to endure further pain, albeit on a much smaller scale than last week.

The FTSE 250 edged higher during the first hour, but always looked vulnerable, as its heavy exposure to tech stocks eventually dragged the index down to finish a net 38.9 down at 6,219.4.

It was the same story for the FTSE SmallCap which lost 19.0 to 2,975.9, additionally weighed down by profit warnings, and the Techmark 100 which finished 50.48 off at a record low of 2,018.45. Its peak was 5,743.

London's refusal to get too carried away was entirely justified, given that global markets are bracing themselves for today's crucial decision on US interest rates. That sees the US Federal Reserve's open market committee meet in Washington to deliberate on interest rates.

Dealers and economists insisted that markets had already factored in another cut of at least 50 basis points, and were clamouring for as much as 75 basis points, following the two 50 basis points reductions made by the Fed in January in response to the sudden slowdown in the US economy.

The latest downward spiral in the tech stocks came after more profit warnings from the US, especially from Corning, the fibre-optics manufacturer. That news hit Spirent, while there was further acute pain for Marconi, the telecoms equipment manufacturer, after the group's stockbroker, CSFB, lowered its earnings for the company "an unofficial profit warning", according to one analyst.

Software shares were badly hit again with analysts maintaining that ratings on stocks such as Logica are still too high.