The former US secretary of state was ambushed in the Yorkshire sunshine by Lindis Percy, the veteran opponent of American bases in Britain, as he arrived to give a keynote speech on how to be a leader.

Mrs Percy, a 63-year-old midwife who is one of Britain's most arrested people, hid in a shrubbery at the Great Yorkshire Showground in Harrogate until Mr Powell arrived by car, after missing his train.

Flapping her trademark upside-down Stars and Stripes like an exotic bird, she kept the retired five-star general indoors while frustrated event organisers puzzled over trespass law.

"These are private premises and we've asked her to leave. Can't we make her go?" a bemused security man at the Yorkshire International Business convention asked a police officer - who, like all his Harrogate colleagues, knows Mrs Percy well from her relentless siege of the nearby Menwith Hill US eavesdropping base.

Compulsion was not on the agenda, it turned out, and Mrs Percy was left to patrol the outside of the convention hall while Mr Powell sat reading newspapers inside.

Before he hurried in, she just managed to tell him: "Menwith Hill is a threat to world peace," to which he replied: "It isn't." Further debate was ruled out as Mr Powell's planned pose on the footplate of the Flying Scotsman - brought specially from York's National Railway Museum - surrounded by a legion of British business leaders was cancelled because of Mrs Percy's unwanted presence.

She continued strolling around, saying: "I'm walking in the Yorkshire Dales and that's my right."

Occasionally organisers tried to steer her away by trying to tell her: "This is a private event."

She replied repeatedly: "Well it ought to be very public," before stretching out her flag with its slogan 'Independence from America'.

Inside the hall Mr Powell did not refer to Mrs Percy in his speech, but emphasised the importance to leadership of a sense of mission, something the protester has never lacked. He also acknowledged that US aid to the developing world was insufficient and needed boosting.

"We doubled assistance and tripled it to Africa but it's still not enough," Mr Powell said.

"Yes, we give $20bn a year but that's a small percentage, and it's not growing as fast as it could."

A highly moral day for northern business leaders, whose previous speakers at the annual shindig have included Mikhail Gorbachev and President Clinton, was completed by Archbishop Desmond Tutu who gave the second major address.

He told the convention that business had played a crucial role in the downfall of apartheid in South Africa and should use its huge clout to help prevent social and ethnic divisions in Britain.