A new freight management system will not be ready when the EU transition period ends, an industry body has warned.
The Smart Freight system, which is seen as vital for preventing delays after the Brexit transition on 1 January, will only be in a beta - or test - version.
But the government insists it will be a fully operational digital service.
It has reassured industry that the system will be operational by December.
The Smart Freight system ensures that trucks are carrying the correct documentation before they travel to ports.
The new system is designed to reduce delays at ports, and to better manage traffic into Dover and queues of lorries building up along the M2 and M20 motorways in Kent.
Truck drivers could face a fine if they arrive at ports without the proper documentation, but the government insists this will be a last resort, and unnecessary if they follow the rules.
Logistics UK, which represents freight businesses, said it was informed by government officials on Monday that a beta - or test - version would be available in December, but would not be fully operational until April.
In a statement, the Director of Policy at Logistics UK Elizabeth de Jong said it was unacceptable and a "massive blow to UK businesses and the economy".
But the government now says "beta" is a standard labelling practice for a digital service that is fully operational.