By Andrew Bryson
Business reporter, BBC News
The FTSE 100 has become dominated by commodities and resources firms
The London stock market is acutely vulnerable to a decline in oil and commodity prices, research carried out for the BBC has suggested.
Analysis by Digital Look for BBC Radio Five Live's Wake up to Money programme shows how the make-up of the benchmark FTSE 100 index has changed.
Before the credit crunch, commodity shares comprised 25% of the total £1.65 trillion value of all the firms listed.
This has now risen to 36%, equivalent to £533bn of its £1.48 trillion value.
Bucking the trend
The contribution of oil, gas and mining stocks to the value of the FTSE 100 has increased 40% in the past year against a backdrop of soaring crude prices and the start of a pronounced slowdown in the global economy.
"15 companies from the oil, gas and mining sectors now make up well over a third of the FTSE in terms of market capitalisation," said Richard Leader, head of marketing for Digital Look - a financial information website.
"If there's a correction in prices or worse, if the commodity bubble bursts, the FTSE is likely to see a big drop."
In the past year shares in many consumer-facing companies in the FTSE 100 have fallen dramatically.
Among leading banks, HBOS shares have fallen 69% while Barclays have dropped 52%.
On the high street, shares in Marks and Spencer and Next have both fallen by more than 45% while shares in pub company Punch Taverns are down 63%.
In contrast, shares in oil, gas and mining companies have soared on the back of rising commodity prices.
Shares in Rio Tinto have risen by 62%, natural gas company by BG 56% while shares in the oil services company Tullow Oil have risen by 113%.
End of boom?
The FTSE100 is calculated by giving each company in it a weighting, which is largely dependent on market capitalisation.
Seven out of the current top ten biggest companies in the FTSE 100 are commodity-based stocks – so a fall in their value will hit the index sharply.
KEY FTSE 100 MEMBERS
Anglo American, BHP Billiton, Rio Tinto, BG, BP, Cairn Energy, Royal Dutch Shell, Tullow Oil
The FTSE 100 fell below the 6,000 mark on Wednesday for the first time since April, caused by a drop in oil and mining shares.
"Sector by sector there are more winners than losers but because of oil and commodities, overall the FTSE 100 fell quite sharply," Mr Leader added.
Commodity prices have soared over the past year, with the price of a barrel of oil doubling to reach a record of $135 this month.
However some commodities have started to fall back from record highs and some experts are beginning to question whether the commodities boom may be cooling.
Gold, which rose to a new record above $1,000 an ounce in March, has since fallen to $877, while copper has fallen more than 11% since hitting record prices in April.