The spread betters are predicting a near 200 point fall in the FTSE 100 when it opens as fears of a debt default by Greece begin to crystalise into a reality.
IG is expecting a 192 point plunge to 6,561.7 in Britain’s blue chip stocks index.
Overnight in Asia the major equity indices were hit hard with the Shanghai Composite, Hang Seng and Nikkei down 3.7%, 2.8% and 2% respectively.
The euro fell almost 2% on the prospect of Greece being forced to exit the single currency, which is now trading at parity with the US dollar.
Greece’s banks are to remain closed today and capital controls will be imposed, Prime Minister Alexis Tsipras revealed yesterday.
It followed the news that the European Central Bank won’t increase emergency funding to the country, which is due to repay around £1.1bn the International Monetary Fund on Tuesday.
Default would move it closer to ejection from the euro.
While cash machines are being kept stocked, there are long queues to make withdrawals.
Greece’s banks are set to remain closed until July 7, two days after its people go to the polls vote on a bailout deal tabled by creditors.
PM Tsipras described the proposal as "an insulting ultimatum" and is hoping a strong no vote will strengthen his hand in further negotiations.
The Greeks rejected a five-month extension to Greece's bailout deal in exchange for reforms.
“A ‘no’ vote is a straightforward rejection of the EMU [economic monetary union,” said Chris Weston, analyst at IG.
“However, it is clear that the current Greek leadership is not compatible with the EU’s top dogs.
“There seems a strong disconnect between remaining in the union with Tsipras and [finance minister] Varoufakis providing direction and the EU providing any aid, which is of course the area we most need to see a new proposal re-established!
“A ‘yes’ vote is therefore where the confusion lies and this seems the most likely outcome.”