If customs from the EU have to be declared, there will be significant delays at British ports, turning them into â€˜lorry parksâ€™, the WSTA warned.
Currently, only imports and exports from outside the EU are subject to customs controls.
But, if the UK leaves the customs union as well as the single market following its two years of Brexit talks, the volume of cargo subject to inspection at British ports will more than double, according to the WSTA. Ministers plan to trigger Article 50, marking the start of negotiations, on Wednesday 29 March.
The WSTA also warned of a risk of a resurgence of alcohol smugglers, if it proves difficult to get wine and spirits in and out of the UK.
â€˜There must be clear and workable mechanisms in place to allow cross-border trade of wine and spirits from the moment we leave the EU,â€™ said Miles Beale, chief executive of the WSTA.
â€˜Anything else will result in huge delays at the ports leading to backlogs and gridlock.â€™
The UK is the second largest importer of wine by volume, after Germany, and second in value, after the US, according to the WSTA.