The gruff voice at the other end of the phone sounds panicked. “I'm in court at three,” the man says, his words cracking with anxiety, “that's less than three hours' time. I'm worried we're going to lose our house”.

John is a middle-aged former police officer, signed off sick and waiting for reconstructive surgery after an injury at work. He is about to appear before a judge for a second time over the £30,000 of arrears that has built up on his mortgage payments. With four children and a partner at home he is terrified of what happens next. “Do you think I can request a stay of eviction?” he asks, clutching at a final straw.

He is on the phone to Mark Cook, one of 50 housing advisers that man Shelter's housing helpline in Sheffield. Backed into a corner, John now owes tens of thousands more on his sub-prime mortgage than the value of his house and has stopped being able to pay after the lender suddenly put up the amount of the arrears he was expected to pay each month.

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After reeling off several sections of the Housing Act for John to quote when he comes to plead his case and ask the council for help, Mark explains as gently as possible that if a judge does decide to pass an eviction, any motion to delay it is unlikely to be granted.

The scale of the nation's homelessness crisis is laid bare in figures published exclusively in The Independent today which show that the numbers calling the housing charity Shelter for help is at an all-time high of almost 175,000 calls in the last year, up 10 per cent on the previous year. Visits to the advice pages of the charity’s website are also up more than 20 per cent, with almost 400,000 people seeking help online.

The latest Government figures show statutory homelessness is up 6 per cent, while the number of households living in temporary accommodation such as B&Bs is at 56,0000, up 9 per cent on last year. Some 80,000 children are expected to spend Christmas without a proper home.

Sasha, a single mother from London, calls in to explain that she has been homeless for a year after leaving her mum's house following a destructive few months of the two “clashing heads”. She gave the local authority her baby's birth certificate and they said she was on a waiting list for a home but it never came through. “My case-worker just ignores me. It's bearable but I'm sleeping on a mattress on my friend’s floor with my child and I'm working hard.”

Helpline staff believe the impact of welfare reforms – including the benefit cap, the ‘bedroom tax’ and increasingly punitive benefit sanctions – could be one the reasons behind the marked rise in calls for help. The continued fallout from the recession, the rise of the cost of living and an apparent increase in rogue landlords as the rental market grows have also contributed.

Liz Clare, a team leader who has been working in the call centre for nine years, says the difference has been marked in the last year. “I think there are a lot of reasons for the rise – there have been a number of changes to people's personal circumstances as well as welfare reform and changes to legal aid. People don't know where to go to for help and we're free.”

The charity says it is expecting a surge in calls in the run-up to Christmas. Last year more than 12,600 people called the helpline in December, a 15 per cent increase on the previous year.

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As evening approaches, calls to the Sheffield centre get more desperate. One man with learning difficulties appears to have had his benefits sanctioned and has been kicked out by his landlord.

“They’ve messed up my money”, he says, “I was claiming job seekers allowance, but not anymore”. Chris Rhodes, the adviser on the other end of the line finds several local shelters and support services for him to go to.

Many of the calls are also about the impact of poor quality rented housing, where cost-cutting landlords would rather leave their tenants in dank conditions than reach in their pockets. In one, a woman describes how a vent in her kitchen wall was missing, leaving a gaping hole to the outside, stuffed with plastic bags and letting in the winter cold. In another, a child's bedroom walls are soaking with damp, but the housing association refused to sort the problem.

Emma Reynolds, Shadow Housing Minister, said: “David Cameron promised to tackle homelessness but on his watch it has risen by a third and the number of families with children living in bed and breakfasts is at a 10 year high.”

A Ministerial spokesman pointed out that homelessness in “is around half the average level it was under the Labour Government.” However, the number of people ‘accepted’ as homeless only refers to those officially recognised by local authorities as such, and this measure has been rising steadily since 2010.

He added: “We are investing £470 million in homelessness prevention from 2011 to 2015 — with funding going to all local authorities and the voluntary sector.”

* Names have been changed to protect identities