Shoppers are braced for more price surges after Russia again blocked grain supplies from leaving Ukraine.
The Kremlin has suspended a deal allowing vital shipments via the Black Sea, after drone attacks on its ships in Crimea on Saturday.
Ukraine, one of the world’s major grain exporters, said Russia ’s claims are a false pretext.
And US Secretary of State Antony Blinken accused Moscow of "weaponising food".
The July deal between Russia and Ukraine to unlock exports was critical to easing the food crisis caused by the war.
It has led to the invaders pushing out of key eastern areas such as Lyman in recent weeks.
A new blockade will send wheat prices soaring again, after 10 months in which nearly all bread and pasta goods have shot up by a double digit percentage.
The Grocery Price Index shows Hovis wholemeal thick bread rose from £1.05 per loaf in October last year to £1.41 this month. Other brands had similar rises.
David Laborde, of the International Food Policy Research Institute, said wheat could rise by 10% when markets open today.
He warned: "Food is already expensive and this is going to make it worse."
Last month, staples such as milk, butter, cheese, meat and bread rose by up to 42%. Russia accused Volodymyr Zelensky ’s forces of carrying out the "massive" 16-drone attack on its fleet in Sevastopol, damaging a minesweeper.
Leaders in Moscow also claimed British naval specialists had overseen Saturday’s blitz – and helped in the blowing up gas pipelines last month.
The MoD hit back: "To detract from its disastrous handling of the illegal invasion, the Russians are resorting to false claims of an epic scale."
