They are either some of the sweetest images of childhood innocence, or they are the first photographs of little girls seen through the looking glass of suppressed paedophile desire.

Whatever the verdict, the government yesterday stepped in to block the sale of the photographs which a stammering, socially inept academic named Charles Lutwidge Dodgson - better known as Lewis Carroll - took of the "dear little girl" who was to inspire his Alice In Wonderland.

Long the subject of intense scholastic debate, and of more prurient public speculation, Dodgson's relationship with Alice Liddell, the daughter of his employer, the dean of Christ Church, Oxford, has always raised uncomfortable questions.

A pioneer and an early master of portrait photography, Dodgson shot Alice - the first of his many child friends - in several ambiguous poses, conferring upon her a kind of adult knowingness.

One of the pictures now features in Exposed: The Victorian Nude, the new exhibition at Tate Britain in London. The 13 glass negatives and prints, which attracted a temporary export ban from the arts minister, Lady Blackstone, yesterday, show Alice and her siblings in a variety of romanticised settings. She is seen lying on a couch in one: in another her sister Ina holds a doll; a further photograph is entitled, in a rather unsettling way, Open Your Mouth And Close Your Eyes.

The work was sold in June when a large hoard of Alice memorabilia was sold by her family. It included her wedding ring, and the letters Dodgson wrote to her - one, half jokingly, asking for a lock of hair - and her mother poignantly requesting her address when she had grown up.

Among the treasures that went to auction was the child's own copy of Alice's Adventures Under Ground, the story which formed the basis for Wonderland and which Dodgson wrote after their first brief meeting in July 1862 when he took Alice and her sisters on a Thames boat trip and amused them with a story.

"Oh, Mr Dodgson, I wish you would write out Alice's adventures for me," she pleaded. He did, inscribing her copy to "whose namesake one happy summer day inspired this story".

Although Dodgson's pictures of Alice, particularly those of her as a child-woman waif, have been reproduced widely, only 30 photographs survived from the time of their brief, intense, and to modern sensibilities, inexplicable friendship, making the loss of half of them to foreign collectors yet more of a blow.

Lady Blackstone said that given the dual importance of Dodgson, as a literary and photographic genius, she hoped the prints, worth more than half a million pounds, would be kept in this country.

"Lewis Carroll's Alice stories are known and loved throughout the world," Lady Blackstone added. "They are regarded as classics of English literature enjoyed by children and adults alike. More and more people who have read them know of the connection between their author and Alice Liddell.

"These photographs are an important part of our cultural heritage, taken by a widely acknowledged pioneer of photography. I very much hope they can stay in this country."