The unprecedented events of recent weeks and the financial fall-out have naturally overshadowed many issues that would normally have received a substantial degree of attention.

One of these is the most recent quarterly set of changes to the constituents of the FTSE 100 - Britain's premier stock market index.

Becoming a member of the FTSE 100 is more than just a coveted badge of honour for any company.

Membership brings with it a much higher public profile for the company, as well as ensuring that a much wider range of institutional investors will consider investing in its shares.

Indeed, the share prices of most companies that enter the FTSE 100 benefit from promotion to the index.

The typical pattern is one where the share price rises in the weeks prior to entry and then slips back a little immediately after entry.

Entry to the FTSE 100 is based on a company's market capitalisation, assuming companies are registered in Britain in the first place. Changes are made on a quarterly basis and the most recent set of changes were made on Friday, September 21st.

From late 1999 to date, the number of promotions and deletions from the index has increased sharply due to the boom in the technology, media and telecom (TMT) sector.

In addition, the extreme volatility associated with TMT stocks meant that several companies were yo-yoing in and out of the index. Baltimore Technologies provides a prime example as it was quickly relegated from the index following its initial entry, only to be re-promoted in the following quarter as its share price regained its previous peak.

However, since late last year, the relentless bear market in TMT stocks has meant that many of the "new economy" stocks have been demoted from the FTSE 100 and most seem unlikely to gain re-entry.

In the case of Baltimore, the story has been one of further demotion from the FTSE 250 to the FTSE 350 as its market capitalisation continued to contract due to a succession of profit warnings. The company is now battling for its very survival as it races to achieve break-even before its cash runs out.

For many Irish investors, the rise and fall of Baltimore, from start-up to membership of the FTSE 100, has been a very dramatic corporate story. However, the recent fall from grace of Marconi (formerly GEC) in Britain puts the experience of Baltimore in the shade.

From 1961, Lord Weinstock built GEC into a leading British industrial group with a global reach. It was viewed as a very solid, if somewhat boring, investment by the investment community.

Many of its businesses were cash cows and the company typically held substantial assets in cash.

During the late 1990s, Lord Weinstock's successor, Lord Simpson, sold off GEC's defence businesses and refocused the group as a telecom equipment manufacturer for the telecom sector.

In the process, the company was renamed Marconi and was reclassified as a technology company.

Investors were enthusiastic with this makeover and Marconi's shares reached a peak in excess of £12.50 sterling (€20).

During the course of this year, as bad news battered the telecom sector, the share price declined sharply but, up to a few months ago, it was still trading above £3.

However, the recent announcement of huge write-offs and the sacking of its chairman and chief executive has led to a collapse in its share price to around 30p, a fall of an incredible 97 per cent from its peak.

The recent general market collapse has brought the share price to an even lower level of 20p.

Marconi is but one of a list of previously high-flying TMT stocks that were relegated from the FTSE 100 on this occasion.

Others that were relegated include Carlton Communications, MISYS, CMG, Colt Telecom and Telewest Communications.

The replacements come from the "old economy", and this time last year they would certainly have been considered by many as a pretty dull and defensive list of companies.

The largest on the list is the tobacco company Gallaher Group, which is now ranked around the 75th largest British company.

Others to gain entry to the FTSE 100 include Northern Rock, Enterprise Oil and British Land.

This latest re-jigging of the FTSE 100 index marks another milestone in the dismantling of the "e-economy" stock market bubble.

It marks further confirmation that the economic slowdown evident even before September 11th has been of sufficient magnitude and duration to decisively burst the TMT share price bubble, and it is now back to basics when it comes to investing in the stock market.

Investors will of course continue to invest in technology but the share prices of these companies will depend on the traditional fundamentals of profits and cash flow in the current harsher economic climate.

Therefore, it seems to be only a matter of time before the somewhat artificial "new" versus "old" economy distinction fades into oblivion.