A Nigerian "witch-hunter" barred from entering the UK has threatened to sue her critics for £500m over claims she stated that a child who cries at night is possessed by Satan - in fact she was referring to possession by the spirit of a vampire.

Helen Ukpabio - who is known as Lady Apostle - is head of Liberty Foundation Gospel Ministries, a group that offers "disconnections" from alleged possessions.

The evangelical Christian, who claims to be a former witch herself, has drawn criticism for exploiting superstitions and potentially harming children. Among other things, she believes children under two years old who cry in the middle of the night might be possessed with black, red and vampire witchcraft spirits.

But Ukpabio, whose ban from the UK was made on the grounds of child protection, is now threatening to sue the British Humanist Association (BHA) and the Witchcraft and Human Rights Information Network (WHRIN) over the wording of complaints against her, which confuse possession by Satan with vampire spirit possessions.

The associations accused Ukpabio of writing: "a child under two years of age that cries at night and deteriorates in health is an agent of Satan".

However, the Christian preacher claims it is "vampire witchcraft spirits" the children would be possessed by, not Satan. She is considering a defamation claim as the public may now believe her to be an "evil woman".

Andrew Copson, BHA chief executive, told the Independent: "The fact that she is threatening to launch a legal claim for half a billion pounds over an alleged distinction between being accused of exorcising 'Satan' or 'Vampires' tells you all you need to know about Ms Ukpabio."

"Given her baseless identification of features of 'possessed children' and her dangerous and irresponsible teachings we feel a strong moral duty to point this out and will not be deflected by libel suits from wealthy 'witch-finders'."