Gordon Brown today calls for "immediate action" to ensure families can afford to live through the cost of living crisis.
The former PM makes the intervention in the introduction to a report by Loughborough University, which warned the government's flat-rate handouts will fall short of allowing families to cope with skyrocketing prices.
For an out-of-work family with two children, the combined loss of the Universal Credit uplift, a below inflation uprating of benefits and a further jump in the energy price cap amounted to nearly £1,300.
If higher inflation for worse-off households is taken into account, it could be as much as £1,600.
But the government's payout comes to just £1,200 per household to those on low incomes.
"The larger the household, the bigger the loss, and a couple with three children is losing almost as much again from rising prices as they did from last year’s cut in the UC uplift," the report reads.
"Flat-rate payments undermine UC’s purpose of basing payments on household size."
In the introduction, Mr Brown wrote: "We have heard from the families we’ve met and those highlighted in the report that the flat-rate payments offered by the government won’t stretch far enough for families who each have different needs and circumstances.
"These must be the people the next Prime Ministers prioritises as we look for solutions."
Polly Jones, head of policy and research at the Trussell Trust said: "Shockingly, food banks in our network are now providing an emergency food parcel to someone every 13 seconds.
“While we welcome the former Chancellor’s support package in May, more must now be done to keep pace with growing living costs especially as we head towards the colder months."
A Government spokesperson said: "We understand that people are struggling with rising prices, which is why we have acted to protect the eight million most vulnerable British families through at least £1,200 of direct payments this year, with additional support for pensioners and those claiming disability benefits.
"Through our £37 billion support package we are also saving the typical employee over £330 a year through a tax cut in July, allowing people on Universal Credit to keep £1,000 more of what they earn and cutting fuel duty by 5p, saving a typical family £100."
