The phone rings: it could be another beaten child or an abused daughter

"Oh dear, yes, I have been busy."... "So you're saying the child has sleeping difficulties. Is that it?" ... "I appreciate you're at the end of your tether." ... "How high was the cupboard?"

The crisis calls come thick and fast - more than 139,000 a year. "Mary" is one of a team of 32 telephone counsellors who answer as many of the calls as they can - 57,000 a year. That leaves 82,000 cries for help unanswered.

A total of 7,621 of the 57,000 Child Protection Helpline calls answered last year were concerning child abuse, be it sexual, physical, emotional or neglect. The other 49,379 were about child care - from requests for NSPCC information, requests for legal advice to reports of adult survivors of child abuse.

On average, the helpline - which costs pounds 1m a year to run - refers between 100 and 120 cases each week to the social services, police and its own child protection teams and projects. The phone bill alone is pounds 90,000.

Mary, 59, is a trained social worker who joined the NSPCC Child Protection Helpline six years ago.

To callers, she is just an anonymous voice. But Mary is also a human being with feelings and emotions of her own.

Spending all day listening to other people's concerns has left Mary reluctant to speak of her personal affairs. "I didn't know I thought all this till I said it out loud to you," she said, interrupting herself.

"I am human. So when I put the phone down, say after a 45-minute call, I can be quite moved by what the person said to me. I can't just pick the pieces up and deal with something else - I've no idea what it's going to be - so I gate the phone for a short time while I empty my head a bit."

She has been in the NSPCC headquarters, near Cannon Street tube station in London, since 9am. Whatever time of the day or night, on whatever day of the year, the scene is the same. It's a timeless zone, up and running 24 hours a day, 365 days a year.

The office is unglamorous. Six desks with six headsets, telephones and computers on them in a medium-sized room looking out on a grim, concrete car park. Rows of multi-coloured information files for different areas of the country line the far end of the room, above which is a large digital clock displaying both the date and the time.

In contrast to the predictable surroundings, no one knows what to expect when they pick up the phone.

"The phone rings and it could be someone saying: `I hear this child next door crying all the time and a lot of banging. I don't want to get involved, here's the address," said Mary.

"Or you could get a mother who has just found out that her daughter has been sexually abused by dad. I'm just holding her distress and, really before she has realised it, realising that there are going to be so many ripples from that allegation."

Mary listens, takes notes and provides the caller with the necessary information where she can. She never talks about herself to callers. "I'd never ever say to anyone `I had an accident and felt like that', or `I've got daughters, I know what you mean'. I don't think people want to know about me."

If a call comes through at 12.25pm, her 12.30 lunchbreak is postponed. Sometimes it's hard to go back to work after the break.

Tears welled up in her eyes as she admitted: "If the callers have been particularly distressed in the morning there's a danger of thinking: `Is everybody like this? Is any child safe? Is there nothing light about this job?' Occasionally I might feel like that, but once I get back on the telephone, you start again."

After Mary logs off, she tries to forget her work. Sometimes that's hard. "We don't get much feedback. We often don't hear what happens," she said.

At other times it is easier. "When someone rings back, be it to say `Yes, the child left on its own,' or `Yes, the father's arrested, she was sexually abused', it's only then you realise how valuable your intervention has been."

The Child Protection Helpline costs pounds 1m a year to run. The phone bill alone is pounds 90,000 a year. Please give generously.

t If anyone has any concerns about the welfare of children then they can contact the national child protection helpline at any time. The freephone number is 0800 800 500.