Analysts at Societe Generale have warned there is a "high risk that the UK could vote to leave the European Union" this year.
In a note out last night, Soc Gen said it is placing a 45 per cent probability of "Brexit", something analysts said would result in "significant economic damages".
"To date, financial markets seem to have taken little notice of this event," they wrote. "To our mind, there is a high risk that the UK could vote to leave the European Union."
Soc Gen analysts estimate Brexit would wipe between 0.5 per cent and 1 per cent off of the UK's annual GDP for at least a decade, with the Eurozone also suffering from an output loss ranging from 0.1 to 0.25 per cent.
Pro-EU campaigners welcomed the Soc Gen analysis, with Stronger In executive director Will Straw saying: "This is yet more evidence that Britain is stronger and better off in Europe than we would be out on our own.
"Jobs, trade, low prices and investment all benefit from Britain’s EU membership and experts are lining now up with fresh evidence supporting Britain's continued EU membership."
"Those campaigning to leave the EU are losing the economic argument because British businesses and families would be worse off outside Europe. Economic growth and opportunities for future generations would all be at risk if we took this leap into the dark."