The head of a freight software company has warned shippers to brace themselves for major disruption when UK customs switches a new processing system on July 1.

Peter MacSwiney, chairman of Agency Sector Management (UK), warned a conference near Heathrow Airport that current plans to implement new regulations, based on the new harmonised SAD (Single Administrative Document) could lead to a disaster as freight forwarders and their staffs grapple with unfamiliar customs declarations and "largely untested software".

Shipping lines and other carriers may refuse shipments where information is incomplete because they could be subject to fines, the way airlines are when they land passengers with incomplete documents, he said.

Mr MacSwiney urged HM Revenue and Customs (HMRC) against implementing its plan for an instant industry-wide application on July 1 and instead urged it be phased in gradually so all are satisfied the software works and shippers are trained in the new procedures.

"Under the new system, current customs declarations won't be accepted. HMRC's original plan was to run the old and new systems together between March and July, giving forwarders the ability to adapt and uncover any defects," he said.

Mr MacSwiney added that freight forwarders might have to demand much more precise information from shippers, possibly at an earlier stage of shipping than is currently the case.

The new system is an EU initiative. It includes numerous new data elements and codes and item-level manifest information. The UK is behind the rest of the EU in implementing it.