Antony Gormley’s wish to make a democratic work of art on the vacant Fourth Plinth in Trafalgar Square was fulfilled in spectacular style this morning as the carefully staged opening of the project in Trafalgar Square was hijacked by an athletic protester.

Stuart Holmes, an unemployed man who has spent 26 years campaigning against actors smoking in films, slipped past four security guards by running along a balustrade abutting the plinth and leaping to grab the safety net surrounding it.

To cries of “Stop him!” and “How the Hell did that happen?” from stunned security guards he swung his legs over the netting and clambered onto the plinth five minutes before the first official participant was due to start.

Boris Johnson, the Mayor of London, chuckled to himself as he prepared to give an introductory speech. “That is art,” he said, admiringly. “It’s exactly what this is all about.”

Mr Holmes, who refused to give his age, stood defiantly with a home-made banner as Mr Johnson and Mr Gormley gave their prepared speeches and the cherry picker lorry waited to lift Rachel Wardell, the housewife chosen to be the first participant of One & Other, the official title for Gormley’s project.

The artist pleaded with Mr Holmes to be gracious and give way to Mrs Wardell when the loading and unloading platform would be raised. “Thank you for your contribution,” Mr Gormley said.

“I hope you’ll have the grace to give way for Rachel, who is our first act. You are the warm up act… You’ve got to understand that this is one person, one hour, so I hope you’re going to give up your place when Rachel comes.”

Mr Holmes shouted back: “Give me the microphone.”

Mr Gormley demurred. “No, no. You should have brought your own.”

The protester capitulated without a struggle, and was applauded as he was brought down on the hydraulic lift flanked by embarrassed security guards. His place was taken by Mrs Wardell, who stood silently holding a lollipop stick marked with the telephone numbers for Childline and the NSPCC helpline.

The crowd of about 100 people did not know which way to look as the cherry picker drove him slowly away, surrounded by a dozen stumbling cameramen from television stations around the world.

The bouncers, who will guard the plinth in rotation 24 hours a day throughout the 100-day duration of the project, stared ahead impassively. “We’re going to have to let him go,” one muttered.

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