Image copyright NSPCC Image caption Marnie works four hours a week as a counsellor

"It's a way to give something back, to feel in that moment that you're making a difference, you're there to listen to children, you're there to help them."

For Marnie, 27, giving up four hours a week to volunteer as a Childline counsellor is a privilege. She says knowing a child trusts her enough to tell her their story is overwhelming.

Childline is urging more people across the UK to volunteer. While it has about 1,400 active volunteers, the charity says 400 more would mean they could answer nearly every child that makes contact.

Currently, the helpline can answer only three out of every four calls or contacts.

Those who can't be counselled immediately are asked to wait in a queue or call or email back at a less busy time - unless their situation is very serious.

'It's taught me to listen'

Marnie has been volunteering as a counsellor for a year and says the experience has helped her learn to listen.

"The art of listening to people has been good," she says.

"We all think we can listen to others and someone telling you about their day or about things that are going on, but I think there's a value in the counselling model and the training you get.

"It really helps you to learn how to listen and pause and let others speak a little bit more than they might have done if you hadn't done that.

"Also, I think, just generally being able to help people reach decisions by themselves - we all have a tendency to think that we can create solutions for others, but actually quite often it's up to everyone to make their decisions in their life - you can help people do that by thinking through all of their options."

So what's involved?

Childline volunteers need to complete 44 hours of initial training and mentoring over a period of a few weeks.

They are then asked to commit to one four-and-a-quarter hour counselling shift at the same time each week for a minimum of one year.

They must also attend regular workshops and debriefs.

Before and after every session, volunteers attend a briefing and debriefing with other volunteers and a supervisor, giving them a chance to talk through the shift and any issues it brought up for them.

Did you know?

The most popular time for children to contact Childline for counselling is between 20:00 and 21:00

This year, half of counselling sessions were between 18:00 and midnight

The most popular day for counselling is Monday

In 2016-17, 71% of counselling sessions were online, compared with 29% over the phone

The charity conducted 295,202 counselling sessions in total last year - 13,746 of these were about anxiety

There are 12 Childline bases across the UK, in Aberdeen, Belfast, Birmingham, Cardiff, Foyle, Glasgow, Leeds, Liverpool, London, Manchester, Nottingham and Prestatyn.

What sort of issues come up?

"It's not one heavy call after the other - there's lots of experiences out there," says Marnie.

"It's easy to forget all the different things that are going on when you're growing up - it can be everything from problems at school, with homework or exams, things like bullying or problems with friends, things in your family and then also dealing with different emotions or pressures in terms of mental health and things like that.

"There are calls about abuse - physical, sexual and emotional abuse as well. We need to be alert to different levels of risk and things like that."

Childline volunteer Michael, 54, says social media is putting young people under a lot of pressure.

"The impact of bullying particularly with social media is relentless," he says.

Image copyright NSPCC Image caption Michael says family breakdown is often an issue

"In my day, there was no social media and bullying stopped at the school gate and you could go home and be safe - whereas now, young people go home and open their phones and laptops and it's still there on Facebook or Instagram.

"There's pressure from school and to pass all these exams. There's this pressure to achieve and to be perfect and it's really competitive - for many young people it can be too much."

Michael says family issues, such as adult relationship breakdown, often prompt a lot of contacts to Childline.

"There are lots of pressures within families because many parents are struggling," he says.

"There could be breakdowns in relationships, parents getting divorced and different families moving into the home - that can make young people feel isolated. They may feel isolated within their family unit."

How do volunteers cope with the stress?

Michael says you find ways to cope with the emotional side of the work.

"With every contact, there's always positives to take out, like the fact that the young person has had the strength to make that call," he says.

"There's plenty of support from your peers but also from the supervisors that run the shifts and there's also a debrief at the end of the shift.

"Then, it's about self-care - in order to support others you have to be in a good place yourself and make sure you look after yourself physically and mentally.

"The way I look after myself is I leave it here. I do the best I can for the young people, I follow all the guidelines, but I leave it here.

"When I go home I keep busy, but I know I've done the best I can while I've been here."

Marnie says: "It can be difficult hearing some of the things that children are telling us - but we've got so much support in the room, we're never taking that call on our own, there's always a supervisor there.

"If you have a particularly heavy call... then you'll have a chat with one of the supervisors immediately afterwards to talk through what you've heard, what your reaction to that is, what feelings you're left with and then, from having that chat, you're ready to go back into the counselling room."

Is it worth it?

Despite having to deal with some tough calls emotionally, Michael and Marnie would definitely recommend volunteering.

"It's incredibly rewarding - I could have had a difficult day at work, travelled 40 miles to get to base, and then do my four-and-a-quarter hour shift," says Michael.

"But by the end of that shift, I'd feel really good about the way we'd supported the young people that had come through. I'd feel quite humble and proud."

Marnie says: "The sense of privilege that you get from having a child trust you enough to tell their story - it's just such an overwhelming feeling that they want to share their story with you, and at the end of it, they thank you for being there to listen to them.

"And in that moment you feel like you helped them just even to take that first step to getting support or that first step to asking for help or understanding their own feelings - it is just such an overwhelming feeling that you're left with."

Children needing help can ring the Childline helpline on 0800 1111 or get in touch via the Childline website.