In the worst five days for the London Stock Exchange since Black Monday 21 years ago, the FTSE lost 24 per cent of its value during the week, wiping more than £250bn off the value of leading companies.

Amid continuing uncertainty on markets around the globe and with increasing fears of recession, the Prime Minister urged other countries to follow Britain's £500bn bank bail-out, while Chancellor Alistair Darling met the world's leading finance ministers in Washington to try to thrash out a joint action plan.

US President George Bush also addressed the nation, insisting: "We can solve this crisis and we will."

But just when there was a chink of light for consumers with the sharply falling price of oil – down from $150 a barrel to about $80 – resulting in several retailers cutting petrol prices and the prospect of cheaper fuel bills, Mr Brown accused oil-producing countries of plotting to cut production to force prices back up. "I'm talking to the leaders of Opec who really are responsible for setting the oil price and telling them that they must not, as some of them are planning to do, cut oil production now so that the price will go up again," he said.

"They must act in a statesmanlike way to help the rest of the world by making sure that we have a stable reduction in the oil price, so that families in Britain and other countries can get petrol at a lower price and gas and electricity bills moved to a better position."

A turbulent week has seen the unprecedented rescue plan for banks unveiled, a co-ordinated global half-point cut in interest rates and warnings from business that recession is looming. Stock markets around the world suffered another bloodbath yesterday, with the FTSE 100 index of leading shares closing below the 4,000 mark – down 8.9 per cent at 3932.1 – for the first time in five years.

City commentator David Buick at BGC Partners said: "It's official. It's a bloodbath – just pure blind panic. Valuations go out the window and sentiment rules."

At the close of trade another £90bn was wiped off the value of Britain's leading shares, and traders said investors are preparing themselves for a global depression. Chris Hossain, senior sales manager at ODL Securities, said: "The stark reality is that markets have judged the co-ordinated interest rates cut not to have been enough, and we are now left wondering how best to get ourselves out of this downward spiral."

European shares also crashed on the back of another slump in US stock markets and hefty falls in the Far East. France's CAC 40 fell seven per cent and Germany's Dax plunged eight per cent. In London, banking stocks suffered the brunt of the fall.

Speaking from Washington last night at a meeting of the G7 finance ministers and International Monetary Fund officials, Mr Darling said it was not enough for countries to "just talk about these things".

"This is a genuinely global problem and we, all of us, all over the world, need to step up to the mark and do something about it," he said.

On a visit to the South-West, including a long-planned engagement at the Cheltenham Literature Festival, Mr Brown defended this week's rescue package, adding: "What we need now is for other countries to do similar things."

Shadow Chancellor George Osborne said it was now essential that the Treasury got on with the implementation of the bank bail-out plan announced by Mr Brown and Mr Darling.