Yuri Gagarin, the first man in space, risked an extraordinary breach in protocol when he deliberately touched the Queen's leg under a table on his visit to London in 1961, according to a new biography of the cosmonaut.

Russia is celebrating the 50th anniversary of Gagarin's historic first manned orbital flight with a raft of events including concerts, a gun salute and flower-laying at his monument in Moscow.

Gagarin, then 27, travelled to Britain as a part of a world tour and was given a hero's welcome in London and Manchester. A statue of him is to be erected on the Mall in London in July to commemorate the visit. The book is written by author and literary critic Lev Danilkin.

It claims Gagarin told colleagues on his return to the Soviet Union that during breakfast at Buckingham Palace he was so in awe of his 35-year-old royal host that he brushed her with his hand to ensure she was not a fiction.

"As a village lad, he only knew about kings and queens from fairy tales," Vladimir Lebedev, a psychologist who worked in the Soviet space programme, recalls in the book: "Yura [Gagarin's nickname] told me he wanted so much to be sure it was a real queen that he touched her under the table, slightly above the knee." In response to being touched, "the Queen just smiled and carried on drinking her coffee," Gagarin told Lebedev.

The book, published as part of the famous Soviet and Russian series of biographies called The Life of Remarkable People, also details Gagarin's struggle to grasp the rules of etiquette in the royal household.

When he expressed doubt over how to use the cutlery in front of him, the Queen apparently replied: "My dear Mr Gagarin, I was born and brought up in this palace, but believe me, I still don't know in which order I should use all these forks and knives." She then added in a whisper: "Each time, you take the knife and fork that lie at the outer edge."

Authors Lev Danilkin, Francis Spufford and Orlando Figes will give a talk titled The Soviet Dream at the Southbank Centre on Wednesday 13 April at 7.45pm.