The UK could save nearly £40bn a year if it left both the European single market and customs union in a "clean Brexit", pro-leave group Change Britain has claimed in a new report.
Change Britain, which is backed by a host of former Leave campaigners including Michael Gove, Nigel Lawson and Gisela Stuart, says cutting loose from all EU regulations and has branded the move a "clean Brexit".
The report forecasts that the UK economy would save £24bn but describes the estimate as "very conservative" and believes the extent of savings could stretch to £38.6m.
Change Britain suggest that by leaving the single market and customs union, the UK could save £10.4bn from EU budget contributions and £1.2bn from "burdensome" regulations while forging £12.3bn in trade deals.
The report follows comments from former Bank of England governor Sir Mervyn King who said Brexit would provide "real opportunities" for the UK as long as it also left the single market.
"This report makes it clear that there are huge opportunities to be had from making a success of Brexit," said Conservative and pro-Leave MP Charlie Elphicke.
"Leaving the EU fully means we won't have to pay billions to bloated Brussels bureaucrats.
"We can build a modern Britain that puts the hard-working classes first and makes it easier for British businesses to trade in the world and succeed."
Theresa May's government is currently split over the question of whether or not to leave the single market.
Supporters of a "soft Brexit" argue that by leaving the customs union and single market the UK could face huge losses in exports to the 27 EU countries, a scenario not taken into account in the Change Britain report.
Britain exported £220bn worth of goods to the EU in 2015, while importing goods worth £290bn.