Video report by ITV News Political Correspondent Carl Dinnen
More than £200 billion has been wiped off the value of shares on the London FTSE 100 since the start of the week, amid fears of a global outbreak of coronavirus.
It's the biggest one-week drop since the 2008 financial crisis, and comes after a British person aboard the Diamond Princess died from coronavirus on Friday.
Global stock markets have gone into freefall with outbreaks appearing in Italy, South Korea, Japan and Iran, raising concerns the virus could become a threat to global trade and industry.
Anxiety intensified on Friday after the United States reported its first virus case in someone who had not travelled abroad or had been in contact with anyone who had.
Both the Dow Jones Industial Average and the S&P 500 fell 1.8%, and the Nasdaq fell 1.7% on Friday.
France's CAC 40 tumbled 2.7%, in Germany the DAX fell as much as 5% before stabilising and Tokyo and Shanghai closed 3.7% lower.
Markets in China and Hong Kong had been doing relatively well despite virus fears.
Mainland markets were buoyed by promises of lower interest rates, tax breaks and other aid to help revive manufacturing and other industries.
But now, major companies are issuing profit warnings, saying factory shutdowns in China are disrupting supply chains. They say travel bans and other anti-disease measures are hurting sales in China, an increasingly vital consumer market.
In Asian trading on Friday, the Nikkei 225 in Tokyo tumbled 3.7% to and the Shanghai Composite Index also fell 3.7%.
The Kospi in Seoul fell 3.3% and Sydney’s S&P-ASX 200 sank 3.2.
The market’s sharp drop this week partly reflects increasing fears among many economists that the US and global economies could take a bigger hit from the coronavirus than previously thought, weakening consumer confidence and depressing spending.