DEREK Acorah was six years old when he had his first psychic experience. It was on the landing of his grandmother's Victorian terraced house in Liverpool as he rushed down the stairs, having been called for tea.

"This man just suddenly walked through one of the open doors. It was because he was a stranger that it shocked me," recalls Derek, 56. "Then he spoke to me and ruffled my hair and told me a couple of things."

When Derek ran downstairs to tell his gran she soon realised that he was describing his late grandfather, who had died at sea two and a half years before he was born. He never took on board that he had seen a spirit, he says, because his grandmother never explained to him what he had seen. But he remembers his grandmother's words regarding his future.

"She said to my mum 'well he's the next one after me' because my gran was a medium."

The next time the episodes started was when he was nine or ten, sitting on the toilet of all places. "A face came out of the doorway and went past me and then a number of faces did the same and it just frightened the life out of me. My gran told me they were helpers, guides in spirit. I can remember at the age of 11 saying to her, 'I don't want to be a medium' and she said you will develop and you will develop naturally'."

Derek left school at 15 and was signed up to the mighty Liverpool FC under his hero Bill Shankly, but it wasn't too long before he proved his gran right.

His time with Liverpool was enjoyable but he never made the first team and he moved to Australia to play football. When he suffered a knee injury at 27 he was set for a career in coaching, but returned to Liverpool, with the voice of his gran in his head on the Qantas Airways flight back to England. "She kept on coming into mind and saying 'remember, you have to have courage'. "

Derek, of Southport, near Liverpool, began doing readings for people by putting an advert in his local paper, the Liverpool Echo. He did about seven in his first week, triple the amount the second and by the third he had no need to advertise ever again. By this time he had his spirit guide, Sam, with him, an Ethiopian he says he met in a previous life. As well as being a guide, Sam acts as a communicator when spirits come through to speak to Derek to pass on messages to loved ones. It was Sam who popped up in Australia and told Derek they were getting close to him returning to England - this was before his knee injury.

"He's always around," says Derek. "Years ago I used to quite freely and honestly talk back to him and I suppose people were looking at me strangely, but I'm very, very conscious these days."

Why would he be conscious?

"Well I'm only conscious when I'm with people who know who I am and what I do. They might find it a little bit difficult to accept," he says.

It's hard to imagine Derek being self-conscious. He has been a familiar face on radio and television for 11 years - starting off with a televised Friday night live show in Liverpool after the producer learned about him through her aunt.

But it is his series on Living TV, Most Haunted, for which he has become most famous. The premise is to travel around various places in Britain, camera crew in tow, holding paranormal investigations. It has attracted a huge cult following, fuelled by regular doses of ex Blue Peter presenter Yvette Fielding looking like a startled rabbit in full night vision. Things often go bump in the night, and on one particular gripping episode, they did more than go bump.

On Halloween 2004, the team went to Pendle Hill in Lancashire, the site of the infamous Pendle Witches. It was here in the 17th century that 19 people were accused of witchcraft and put in a dungeon 30ft underground. By the time they came to be tried five months later they could barely speak. Ten of them were hanged on August 20, 1612.

It was the closest Derek came to being afraid, not counting when he first saw his deceased grandfather on the landing.

"That was a nasty one," he shudders. "They had all been practising witches. One of them was the daughter of the one who ran the coven and she used to do all kinds of things to babies, cut their hearts out, drink their blood. It was nasty.

"It wasn't just affecting me, it was affecting most of the crew. One of them felt as if he had a ligature around his neck, as if he was being strangled. My last words to the people living in the building were to do the cleansing (exorcism) almost straight away".

He has now written a book, Ghost Hunting with Derek Acorah, encouraging other people to go and find some ghosts. It contains details of the types of ghosts you can encounter - ghosts who appear on anniversaries, poltergeists etc - famous ghosts of the past and the places across the UK and abroad where you can find them. There's even a section on what tools you'll need for the job.

"You're talking about a digital camera, an ordinary camera, a couple of candles, heat sensing apparatus... More than anything if you can take a dog along that's best. Because most dogs use their senses purely they're very, very aware of the temperature drops, when spirit people are around."

But is it advised for people to go ghost busting if they could be in danger of meeting terrifying types like the Pendle Witches?

"The places I've given them are places where they can gently start to get experience with the camera and with orbs" (believed to be spirits which sometimes appear as specks of rain or light on a camera lens). They're not going to come across anything like that."

Another aspect of Derek's work is his live shows. Could his shows be seen to be exploiting his audience, preying on those who have been bereaved?

The question stirs a passionate rebuke.

"People who make those statements are ignorant," he insists. "After 27 years these ignorant minded people will never stop Derek Acorah or any other medium. In the old days they dunked us in water or burnt us at the stake. We're not doing anything evil. I think people should try and find out about it and go a little deeper."

Derek believes in God, has done readings for many clergy including an archbishop whom he won't name. He also believes we're reincarnated, going back to the spirit realm when we die.

When he's not working, he can switch off the voices, so to speak. "I only open up when I'm working, otherwise it would be terribly draining."

He is married to Gwen and has a step-daughter Jane, and son Carl, along with grandchildren Daniel, 13, Rebecca, four, and Jessica, seven.

So are any of them showing signs of being a spirit medium like their famous grandfather?

"Daniel has it," he says. "But he doesn't want to know. I think somewhere along the line in his life maybe the spirit calling will be too strong for him to ignore." And when this happens, his grandfather will be there to guide him.

* Ghost Hunting with Derek Acorah (Harper Element, £7.99).