PARIS (REUTERS) - France will test run measures it has prepared for Britain's exit from Europe for a month so that companies are fully prepared ahead of Britain leaving the bloc at the end of October, its minister-in-charge of customs said on Friday (Aug 30).

Gerald Darmanin will meet Michael Gove, the British minister in charge of coordinating "no-deal" Brexit planning, in Calais later on Friday to show how France is preparing for Britain's departure from the EU on Oct 31.

Businesses have been warning of long tailbacks for lorries transporting goods between mainland Europe and Britain, and the British government has said most goods from the EU will be allowed into Britain without full customs checks for at least three months if there is a no-deal Brexit.

"For a month we will act as if there is Brexit for a large number of companies. We're going to put in place a sort of general rehearsal so that we are ready at the end of October," Darmanin told RTL radio.

About 700 extra customs officers have been drafted in and the authorities will also introduce online border declarations forcing companies to announce their goods prior to arriving at the border.

"You are in Grenoble (eastern France), you are a small or medium-sized company, you export to Britain and so you now declare everything online," Darmanin said.

"There will be barcodes and numbered plates or merchandise... and without stopping at the border, your goods will go directly to Britain. There will be no queues of tens and tens of kilometres."

France is the EU's biggest agricultural producer and exports large amounts of wine, spirits and dairy products to Britain, while relying on its neighbour's waters to sustain its fishing industry.