Quitting the customs union could allow the UK to forge trade deals creating hundreds of thousands of jobs, a pro-Brexit campaign group has claimed.
The Change Britain analysis suggests that free trade deals with countries which have already indicated an interest in signing an agreement could create over 240,000 jobs.
That figure could rise to almost 400,000 if Japan and the south-east Asian Asean bloc also sign free trade agreements with the UK after it leaves the European Union, the campaign group said.
But campaigners advocating a soft Brexit have warned that exports to the EU could be hit by leaving the customs union, potentially costing British jobs.
The Change Britain analysis suggests that the United States, India, the South American Mercosur group, China, Canada and South Korea have all expressed an interest in a trade deal.
Agreements with those countries would create 240,108 new jobs, the pressure group claimed.
Change Britain said it was also reasonable to assume that deals would be struck with Japan and Asean at some point in the future which, on top of the other agreements, would result in the creation of a total of 387,580 jobs.
Change Britain founding supporter and former CBI director general Lord Jones of Birmingham said: "The UK has a rich history as a great trading nation.
"It is therefore no surprise that a number of major economies have already expressed an interest in striking free trade agreements with us.
"The only way we can make the most of these huge opportunities is to leave the EU's customs union and take back control of our trade policy. This will create hundreds of thousands of new jobs in a range of industries right across the UK.
"We can then take our place as one of the global champions of free trade."
A Department for International Trade spokesman said: "The Government is determined to make a success of Brexit. That's why it's right to take time to work out the best options for the UK's trading relationship after we leave the European Union.
"As we have said before, those decisions have yet to be made."