The group says it offers self-development, but people who have left say it's taken over their lives.

They say they've been encouraged to hand over tens of thousands of dollars, separate from their family, and have suffered extreme harassment.

One charity which helps break people free from abusive groups says it receives more calls about the organisation than any other in the UK.

Katrin Nye has been working on the investigation. It's been 18 months since Geoffrey Lee-Jones left Lighthouse International Group, a life-coaching company accused of being a cult.

The 34-year-old sailor from Portsmouth initially got involved with the organisation for business mentoring, but soon he was on the phone to his mentor at all hours of the day. "I thoroughly enjoyed the conversations you and I had.

At first, I was motivated, I was inspired, and I started working hard.

These calls then became more frequent, longer, more intense, more about deeper parts of your life.

In time, I began to share traumatic things, things I found deeply painful." Geoff was encouraged to become part of Lighthouse full-time.

That meant being on group phone calls every day, often led by Paul Waugh, their charismatic leader. "Many people who don't know me very well think I'm a mystic because I'm able to sort of feel things that no one else can." All these calls were recorded, then painstakingly transcribed.

They began to take over Geoff's life.

They got longer and longer as we went.

So within six months, they're five to six hours." "And that's every day?" "Every day." "So, I would listen in at times.

The topics were getting more sinister.

Narcissists, you know, toxic parents.

And then that's when I started worrying because I thought, he's literally being brainwashed all day, every day." People who have been part of Lighthouse have become isolated from family.

Some move into shared houses.

And there's a financial cost, too.

In total, Geoff paid £131,000 to the organisation.

He sold his house to fund some of it.

Lighthouse says that any money paid is a self-investment.

Erin, another former mentee, paid over £35,000. "I took out an interest-free credit card.

And the idea came from my mentor.

I started to feel as though I couldn't think anything unless my mentor said that it's a healthy thing to think." When people start to ask questions, things can turn nasty. "I'm telling you now, you've got to stop doing it.

It's not acceptable, OK?

Treating us as if we're trying to do you over.

It's a cynical little old witch." Lighthouse does not like criticism.

People who have spoken out have been reported to the police.

Lighthouse even contacted the employer of another critic to tell them she was unfit to do her job. "I consider Lighthouse a very classic example of a cult.

Firstly, cults are started and led by a charismatic and authoritarian leader.

But they're also bullies.

The structure is steeply hierarchical, but it's heavily isolating.

Then you have this process of what I call brainwashing, or we could also call coercive control.

If you do this to people, you can then exploit them." Martin's daughter Mel is still part of Lighthouse.

She no longer talks to her family. "One feels so powerless.

You feel, what can I do?

What's it like having a child in Lighthouse?

It's as if my daughter's died because she's not my daughter that I know is not there anymore.

I'm sorry." One week ago, Lighthouse International Group was shut down as a business by a court over a lack of financial transparency.

We put our allegations to their leader. "How do you feel, Paul, about the fact that so many people think you're running a cult?

We're not running a cult because they don't know what a cult is.

If you asked them what's the difference between a cult and a community that supports people, they wouldn't be able to tell you.

Why do you think so many people say it?

Because they're slurring us, they're smearing us.

That's exactly what they do.

Are you going to carry on?

Yes, we are carrying on.

Thank you.

We've had enough.

No comment." Katrin Nye, BBC News.