Dozens of charities on the front line dealing with a “tsunami of need” caused by the cost-of-living crisis have called on the Government to provide urgent financial support to vulnerable households and the organisations that support them.

An open letter signed by 48 bosses in charge of providing a range of services across the voluntary sector said an “economic crisis of a magnitude not experienced for decades” will push many who have managed to make ends meet into poverty.

People who are currently struggling will be “pushed into desperation”, creating an “urgent and growing need” for swift Government action, it added.

The letter said: “We are calling on the Government to urgently deliver meaningful financial support to those in the greatest need, directly to households and through the benefits systems that already exist to provide support.”

It added that charities and voluntary organisations playing an essential role in “keeping people afloat” are also struggling with a range of challenges.

These include the inflationary pressures of the rising costs of fuel, energy and salaries, increasing demand for support which public services are unable to provide, and depleted income from donations.

The letter said: “Many organisations are selling essential community facilities because they cannot afford to keep buildings open, or are expecting to close badly-needed services altogether.

“They are seeing ever greater demands made of them to fill the gap as the NHS and local authorities especially struggle to deliver adequate services to communities.”

Describing the scale of the challenges facing support organisations, the letter said food banks are “working flat out”, community centres are planning to provide “warm hubs” during winter, and disability charities are providing cash to people who cannot wait for help.

It added that other organisations are preparing for growing numbers of people suffering a mental health crisis and increased suicide rates, while more children are predicted to enter care, and animal charities are already struggling to cope with the number of abandoned pets.

“When people cannot afford to pay their bills the consequences go far beyond whether they can keep their lights on at night,” the letter said.

The organisations added that the pandemic showed that “stepping up in a crisis” to provide support “is what charities and voluntary organisations do best”, but warned many may not have the required capacity to meet demand in the coming months.

“Charities have already drawn on their reserves, they have already have already become as lean and as agile as they can possible be, and they have not had the chance to recover (from the pandemic),” they said.

“Many charities and voluntary organisations have little or nothing left to see them through this second tsunami of need.

“This is going to be a tough winter for everyone, but for those in greatest need it will be catastrophic.

“It is essential that urgent action is taken to support those individuals, and to ensure that they are able to access the help that they will need to get them through.”

The letter comes amid growing warnings of the dire impact of the cost-of-living crisis and a lack of clarity over how the Government will respond under the winner of the Conservative leadership contest – either Liz Truss or Rishi Sunak – who will replace Boris Johnson as Prime Minister on September 6.

The letter was organised by the Association of Chief Executives of Voluntary Organisations and signatories include the National Children’s Bureau, National Voices and Disability Rights UK.

A report by the UCL Institute of Health Equity has warned that a “significant humanitarian crisis with millions of children’s development blighted” is on the way if the Government does not act to prevent more than half of UK households plunging into fuel poverty.

The head of Citizens Advice, Dame Clare Moriarty, said on Thursday that people are already being put in “impossible positions” ahead of energy bills rising in October, and warned of long-term consequences for health.