The number of people struggling to buy food has risen by 57% in three months, according to research by the Food Foundation.
The charity said food bank users are increasingly requesting items that do not need cooking because they are worried about how they will afford rising energy bills.
The “chilling” figures come at a time when the cost-of-living crisis is increasingly hitting families who are facing rising utility and food prices, which are outstripping the amount by which benefits have risen.
The last few months have been really tough. I’ve had days where only my daughter ate and I've had her leftovers, if anything at all
Single father Dominic Watters
The charity analysed responses from 10,674 UK adults who were surveyed online by YouGov between April 22 and 29.
Some 13.8% said they or a member of their household had either eaten smaller meals than usual or skipped meals, not eaten despite being hungry, or not eaten for a full day because they could not afford or get access to food in the past month.
Extrapolated to UK population level, the findings suggest around 7.3 million adults live in households affected by food insecurity, including 2.6 million children.
This is up from 4.7 million adults surveyed in January (8.8% of respondents).
The research shows that nearly half of households on Universal Credit have been food insecure in the past six months.
People in households where someone has a disability, households with children and non-white ethnic groups have a higher risk of food insecurity.
There has also been a rise in the number of families with children experiencing food insecurity in the past month – 17.2% in April up from 12.1% in January.
The Food Foundation warned that people will become more reliant on lower cost foods, which tend to be “calorie-dense and nutrient-poor”, which will risk their health and increase obesity levels.
If one household in seven is food insecure, society is failing in a fundamental way
Professor Sir Michael Marmot
It is calling on the Government to increase benefits in line with inflation and expand access to free school meals and the Healthy Start programme.
Dominic Watters, a single father from Canterbury, told the charity: “The last few months have been really tough.
“I’ve had days where only my daughter ate and I’ve had her leftovers, if anything at all.”
Anna Taylor, executive director of the Food Foundation, said the “extremely rapid rise” could be catastrophic for families.
She said: “The situation is rapidly turning from an economic crisis to a health crisis.â¯Food banks cannot possibly be expected to solve this.
“The Government needs to realise the boat is sinking for many families and it needs to be fixed. Bailing out with emergency food parcels is not going to work.”
Professor Sir Michael Marmot, director of the UCL Institute of Health Equity, added: “If one household in seven is food insecure, society is failing in a fundamental way.
“These figures on food insecurity are all the more chilling because the problem is solvable. But, far from being solved, it is getting worse.”
A Government spokesman said: “We recognise the pressures on the cost of living and we are doing what we can to help, including spending £22 billion across the next financial year to support people with energy bills and cut fuel duty.
“For the hardest hit, we’re putting an average of £1,000 more per year into the pockets of working families on Universal Credit, have also boosted the minimum wage by more than £1,000 a year for full-time workers and our Household Support Fund is there to help with the cost of everyday essentials.”
Shadow work and pensions secretary Jonathan Ashworth said: “These are devastating findings that reveal the acute levels of hunger impacting families and children nationwide caused by the Conservative cost-of-living crisis.”