Planning for the new Brexit deadline is “more difficult” because the supply network will be full of Christmas stock, Tesco’s boss has warned.
Dave Lewis told the BBC that the new deadline of the end of October meant there would be “less capacity” for stockpiling longer-life items.
A no-deal Brexit could mean tariffs and delays at the border that interrupt supplies of some food, he said.
But Mr Lewis said leaving the EU could also provide opportunities for the UK.
Mr Lewis said the supermarket chain had bought extra stock of long-life items in preparation for 29 March – when the UK was initially expected to leave the EU – but said it would be harder to make similar preparations this time round.
“We’ll do whatever is practical depending on how things develop between now and then.
“But the challenge will always be those things which are shorter life – fresh produce. That’s what the UK imports quite a lot of,” he said.
He said the impact on shoppers of a no-deal Brexit was still uncertain.
“Empty shelves depends on what no-deal means. If there’s a problem at the border, if there’s a problem with tariffs then there could be interruption.
“If as part of no deal there is no tariff, there is no problem. We could be absolutely fine,” he said.
The UK currently imports about half of the food it eats, but Mr Lewis said Brexit could be a good time to “take stock”.
“It may be a good time for the UK to… decide, actually: what food do we want to eat, with what impact on health, with what impact on the environment.
“Having a food strategy for the country would be a very good outcome.”
Other key challenges facing the supermarket giant are demands for healthy eating, cutting waste and plastic-free packaging.
Mr Lewis admitted companies “don’t ever do enough” to cut plastic use.
While Tesco has removed plastics where it can and introduced the option for customers to bring their own packaging, he said getting rid of it completely would require huge changes across the supply chain which would involve “9,000 suppliers across 35,000 products”.
He warned getting rid of packaging protection for loose goods could mean they were more likely to be damaged, creating more waste, and ultimately higher prices.
“We can’t change everything tomorrow, it’s not practical,” he said.