A celebrity psychic who claims to speak with the dead in sellout shows across the country has been challenged by sceptics to prove her supernatural powers. They have invited TV "star psychic" Sally Morgan to demonstrate her ability to connect with the spirit world in a specially designed test in Liverpool on Monday.

The Halloween challenge is backed by the US paranormal investigator James Randi, and qualifies as the first step towards claiming a million-dollar prize established by the James Randi Educational Foundation for any psychic who can prove their "gift" to be real.

Morgan, whose website offers psychic readings over premium rate phone lines, has written three books and is filming the third series of Psychic Sally on the Road for Sky LIVING.

Sceptic groups, led by the science writer Simon Singh, arranged the test after one of Morgan's shows in Dublin last month at which some members of the audience reported hearing someone at the back of the theatre apparently feeding her information on stage.

Morgan, who claims to have seen her first ghost at the age of four, has strongly denied any fakery and blamed the voices on chattering technicians at the venue. The theatre supported this account in a separate statement.

TV illusionist Derren Brown said: "It's important people don't think that a test is a way of debunking or disproving. It's a great way of anyone making amazing claims to show that they hold up and are not just a result of trickery or self-deception. The test should be both scientifically rigorous and yet fair to the psychic: it would show, if the psychic is successful, that what he or she does is real.

"Such tests are important because it's too easy for a person to fool others (or themselves) into thinking he or she has special abilities. If someone is going to put you in touch with your dead child you'd want to know if they were real, deluded or a scam artist."

The group behind the challenge has enlisted Professor Chris French, head of the anomalistic psychology research unit at Goldsmith's, University of London, to design and conduct the experiment, which, if Morgan attends, will be hosted by the Merseyside Skeptics Society in Liverpool.

"There are still question marks hanging over Sally with regards to how she derives her insights during her readings. By agreeing to our test, Sally has an opportunity to reassure any fans who might doubt that she is genuine in her communication with their deceased loved ones," Singh said.

"This is not a trivial issue, as many vulnerable, grieving and desperate people turn to Sally for support and advice, and it is crucial that these people can be confident that they are not being deceived," he added.

Audiences who attend Morgan's shows can hand in photographs of dead loved ones for her to use on stage. During the performance, Morgan selects a picture and claims to make contact with the deceased, at times adopting their voice to relay messages from beyond the grave.

In the challenge, Morgan will be shown photographs of 10 deceased women and asked to match each to an entry on a list of their first names, by connecting with their spirits. Singh said the test was expected to last 20 minutes. To pass, Morgan will be required to match seven or more names to the right photographs.

A Guardian request to Morgan for comment on the challenge was passed to her lawyers, who did not respond.

"I believe that this opportunity to conduct a direct, simple, understandable test of 'Psychic Sally' and her often-stated ability is an excellent situation in which she will be able to not only establish her claimed abilities, but also move on to earn the million dollar prize that stands ready to be paid out," said Randi.

Professor French added: "It's important for any test to be as fair as possible, and an accurate reflection of what Sally claims to do. Fortunately, the types of readings Sally gives in her live shows lend themselves very well to a very simple test design.

"With the right controls in place, we can perform an experiment where anyone who is deluded or who wants to cheat would find it very hard to be successful, but someone with genuine psychic ability, as Sally claims to have every night in her sold-out shows, should find the whole thing a breeze."

Michael Marshall, vice president of the Merseyside Skeptics Society, said: "At the moment, there's no real proof that anybody is able to communicate with the dead. In fact, no medium has ever, in the history of the human species, been able to reliably demonstrate such an ability. Whilst we're somewhat sceptical of the claims Sally makes, we'd love nothing more than the opportunity to get to the bottom of things, once and for all.

"If Sally really is able to demonstrate in a very simple test that her skills are in fact psychically derived, as opposed to produced via the various magic tricks and techniques we know fraudulent mediums could use to appear to have psychic powers, then we'll be first in the queue to celebrate her talents. But until she can show her readings are genuine, we don't think it's right that vulnerable people are led to believe she's really talking to the dead."

Update: On 20 June 2013 Sally Morgan successfully settled her libel action against publishers of the Daily Mail, who withdrew the suggestion that she used a secret earpiece at her Dublin show in September 2011 to receive messages from off-stage, thereby cheating her audience, and accepted that the allegation is untrue. Her statement can be found here.