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If you were skeptical of the negative affect leaving the European Union would have, they are already happening. Britain's biggest companies are £100 billion less valuable than they were four days ago after several polls put a 'Leave' vote ahead.

The FTSE 100 index dropped below around 121 points below the 6,000 mark on Tuesday. Over the past four days of trading, the index has lost 378 points - the equivalent to £98bn.

Concerns that a Brexit was a real possibility also knocked markets in Germany and France, where the Frankfurt Dax and Paris CAC indexes dropped 1.4%.

In another blow, the pound took yet another tumble - 1.2% this time, giving a real indication of the effect a Brexit would have on the value of sterling.

Elsewhere in a dramatic and unprecedented turn of events, investors flocked to put their money in bonds with the German government. The 10-year bund yield dropped into negative territory for the first time ever, meaning investors are effectively paying the German government to lend to it for 10 years.

The Brexit-induced panic is also causing investors to keep hold of their money. According to a survey by Bank of America Meryll Lynch, global fund managers are sitting of 5.7% of their portfolio in cash - the largest proportion since November 2001.

A separate study found that 71% of investment staff in the UK expect investment portfolios to suffer in the year after a Brexit vote, with just 8% expecting a positive benefit and 17% saying a 'minimal impact' would take place.

Will Goodhart, chief executive of CFA UK, which conducted the above research, said: “Both UK and non-UK respondents believe that a Brexit vote would have a negative impact on UK asset values on a one-year basis. UK respondents feel this more strongly, but it is interesting that qualified investment professionals from around the world – with no emotional involvement in this issue – also strongly believe that a Brexit vote would be against UK clients’ interests over that timeframe."

Economic blogger Michael Baxter said: "The yield on UK government bonds has also fallen to a new record low, but in the short term, sterling may be the biggest victim of a Brexit vote. It is a combination of factors that pose the risk. For one thing, the UK's balance of payments is awful. Under different circumstances sterling would have crashed a long time ago. But investor's ploughing money into the UK meant the pound was able to avoid that fate. There is a danger that a Bexit vote will lead to a reversal of that investment.

"Also, the US Fed may increase rates soon, encouraging investors to withdraw money from the UK and put it into the US. A Brexit vote, on top of these other factors, could lead to sharp falls. As it happens, modest falls in sterling may be positive, giving UK exporters a terms of trade benefit, although a Brexit vote may hit trade in other respects. The danger lies in the possibility of severe falls in sterling, which could trigger off a very serious crisis, indeed."