Of those surveyed, 35 per cent said the transition period should remain as currently agreed, 8 per cent believed it should be shortened, and 40 per cent think an extension is necessary.
Downing Street has insisted that an extension would “prolong business uncertainty”.
The Centre for Brexit Policy was founded by former Conservative Cabinet minister Owen Paterson and John Longworth, the former director-general of the British Chambers of Commerce.
In its report, the think tank warns that a two-year delay to Brexit resulting from another 12 month extension would cost the UK up to £378bn.
The figure is based on the UK continuing to pay £11bn a year to Brussels, a loss of an estimated £132bn in free trade agreements with non-EU countries, and £176bn that could be realised by adopting better regulation.
Writing for The Telegraph, Mr Paterson said he hoped the findings would “re-energise” Mr Johnson’s commitment to end the transition period on Dec 31.
Mr Longworth warned that “the combination of these eye-watering costs and continued subservience to EU rules would wreck any chance we have of restoring our fortunes as a nation as the pandemic subsides.”
With the UK unable to strike trade deals with countries such as the US and Japan while in transition, the report assumes that a potential 3 per cent annual boost to GDP from these arrangements would be lost.
It places the potential benefit of diverging from EU rules at 4 per cent of GDP, or £88bn annually, citing three studies, including one led by the pro-Brexit economist Professor Patrick Minford.
On Friday, David Frost, the UK’s Brexit negotiator, warned that “very little progress” had been made in last week’s negotiations and called on Brussels to drop its demands “level playing field” guarantees on tax, labour rights, state aid and the environment, and status quo access to UK fishing waters under “existing conditions”. Mr Barnier accused Britain of failing to understand the consequences of Brexit.