Mayor Boris Johnson is cock-a-hoop as giant blue cockerel roosts on London's Fourth Plinth

Boris Johnson hailed the new sculpture to adorn the fourth plinth of Trafalgar Square as a monument to British dominance in the Tour de France but warned art lovers may not be able to Google the work under new proposals from the Prime Minister.

The Mayor of London largely succeeded in his promise to stay away from innuendo as he unveiled the 15 foot blue cockerel by German artist Katharina Fritsch, which she has named Hahn/Cock.

The sculpture, which replaced the statue of a boy on a rocking horse by Michael Elmgreen and Ingar Dragset, will remain in the square for 18 months.

Mr Johnson said: “It’s times like this when politicians should resist any artistic interpretation,” before adding after Chris Froome’s victory in the Tour de France, it could be “a symbol of French sporting pride brought like a chicken to London and we have maintained this French cock in Trafalgar Square.”

Referring to the name in the context of recent plans by the Government to tackle online pornography, the Mayor said: “If you were to Google it in a few years’ time, you will probably not be able to find it as that search engine will collapse at the behest of the Prime Minister.” He hurriedly added with a chuckle: “Quite properly, by the way.”

Ms Fritsch, who is from Essen, has been the subject of an exhibition at the ICA London as well as around Europe and in the US, where she has work in the Museum of Modern Art in New York.

She said the work was intended to be humorous but initially had not thought about the French aspect of the work “especially in a place celebrating victory over the French”.

“What it does symbolise is that London is not only the London capital of the world and the sporting capital of the world,” Mr Johnson said, “but the cultural and artistic capital of the world. it is a testament to our sense of freedom and liberty that we have here in London.”

The plinth was built in 1841 to carry an equestrian statue of King William IV, but remained vacant until 1998 when the Royal Society of Arts set up the Fourth Plinth Project. Artists including Mark Wallinger and Rachel Whiteread produced work for the site.

Since 2005 the site has been under the stewardship of the Fourth Plinth Commission after the Greater London Authority took control. The first piece was Mark Quinn’s controversial sculpture Alison Lapper Pregnant.

Other prominent works since then included Antony Gormley’s One & Other in 2009 in which a total of 2,400 members of the public took to the plinth for an hour each over 100 days, and Yinka Shonibare’s Newlson’s Ship in a Bottle.