"Flour is one of those invisible bits of the food chain until it isn't there," said Alex Waugh, director general at Nabim, which represents Britain's millers producing the staple.
Along with pasta, rice and tinned food, flour is hard to come by in UK supermarkets since shoppers began stockpiling in large quantities around a month ago, even before the country went into lockdown.
Despite bread being easy to find on supermarket shelves, Britons are increasingly making their own as the closure of restaurants and takeaways leads to more home cooking generally.
Others are turning to baking cakes to help pass the time. The result has been a doubling of flour purchases to four million packets per week, according to Nabim.
"I don't remember any time like this," said Waugh. Supermarkets have reacted by limiting the amount of packets that can be bought by each customer.
Britain's biggest retailer Tesco is limiting shoppers to three of the same item on its entire range of products, both in store and online. "We're overwhelmed with orders," said David Wright, general manager of flour producer GR Wright and Sons, adding that online orders had rocketed from a dozen to 800 in just two days.
"We had to close the shop," he told AFP. The family company born in the 19th century has to go back to the late 1970s, scene of a UK bakers' strike, to recall such a tense situation.