The mistake arose due to a confusion between the freeport sites themselves and the multiple customs areas that are contained within them.
Freeports are areas near shipping ports or airports where imported goods are free from tariffs.
They are designed to boost economic activity like trade, investment and job creation, and businesses operating in them get certain tax breaks, which include reliefs on property and hiring new workers.
Current freeports are located around ports in Inverness, the Forth, Teesside, the Humber, Liverpool, Anglesey, Milford Haven, Plymouth, the Solent, the Thames, and Felixstowe and Harwich.
However, not all of these freeports are classed as being operational due to them not having “designated” tax and customs sites.
A government official told the BBC that the chancellor is set to confirm five new customs sites within existing freeports, rather than new freeports.
Ports in Inverness and the Humber will get designated customs sites for the first time. The move will make the Humber site operational as a freeport and eligible for tax reliefs and funding, but the Inverness site is still waiting final approval.
The three remaining new customs sites will be in Liverpool, adding to three sites already in place there.
Reeves will still reveal plans for a separate investment zone in the East Midlands, which was also announced on Friday.
The Financial Times, which first reported the error, said Friday’s announcement, made while the prime minister was at the Commonwealth heads of government summit in Samoa, had caused “bafflement” among firms and officials involved in the freeports, as they had not heard of any plans.