Logistics bosses are calling on the Government to help clear congestion at container ports.
A spike in imports due to the Covid-19 pandemic and fears of a no-deal Brexit have led to bottlenecks at UK ports.
The Port of Felixstowe has been suffering congestion for weeks, but the issue has reportedly now spread to Southampton's port.
The problem is being exacerbated by disruption to shipping movements around the world, partly caused by the pandemic.
In a letter to Transport Secretary Grant Shapps, the leaders of organisations such as the UK Major Ports Group, the UK Chamber of Shipping and Logistics UK wrote: "Although we are hopeful that the current peak of port congestion has passed, high volumes remain and could persist for some months, running into the period of the end of the EU transition.
"Therefore challenges remain. The current situation has arisen in part from imbalances that accumulated over months. Reversing this accumulation is not an overnight task."
The letter called on the the Government not to be "complacent", and called for it to provide "sensible flexibilities and easements" around the movement of containers at ports and road haulage.
The Department for Transport said partners across the Government are working closely with the freight industry to resolve challenges in the global container system.
UK Major Ports Group chief executive Tim Morris said: "The Covid-19 pandemic has caused unprecedented volatility in global supply chains. The impact is being felt across the world, including here in the UK.
"The situation at the UK's ports is improving following commitment of extra resources, working closely with customers and ports across the UK taking on more traffic.
"However, we are not complacent. Improvements at UK ports will take time to work through supply chains, they remain very busy and the underlying problem is global."
Car manufacturer Honda said it has paused production at its Swindon factory due to "transport-related parts delays".
It hopes to re-start work "as soon as possible".
The plant will permanently close in July next year with the loss of 3,500 jobs.