Ms Lamb is making her first visit to New Zealand, and was in Dunedin this week speaking about fair trade issues at a series of meetings.
At Otago Girls' High School, she addressed about 40 pupil representatives from six Fairtrade schools, and later spoke to about 800 OGHS pupils at a school assembly.
She also attended a lunch hosted by the University of Otago School of Business and gave an evening lecture, organised by the university's Centre for Theology and Public Issues.
It is this kind of busy schedule and high energy approach that once earned her the nickname "Hurricane Harriet".
She was quick to explain in an interview that some youngsters had been discouraged from following their dreams. But the growing success of the inter-national fair trade movement showed that good ideas, however "mad" they initially seemed, could win acceptance, and ultimately help build a better world.
Some cynics had been quick to dismiss the fair trade movement, initially claiming it would become only a tiny "niche" market involving only a few vicars.
"I think they've been proved wrong."
During her 10 years at the helm of the UK's Fairtrade Foundation, estimated sales of Fairtrade products in the UK have grown from 30 million to 1.17 billion.
Ms Lamb said the Fairtrade message was still gaining momentum, with some big firms, such as Cadbury, also supporting the cause.
A total of $36 million in Fairtrade goods had been sold in New Zealand last year, double that of the previous year, and Fairtrade bananas, introduced here only last year, already held a 2% share of the New Zealand market.
Dunedin was also playing an important role, as one of New Zealand's first Fairtrade cities, and was also home to 10 of New Zealand's 13 Fairtrade schools, she said.
Dunedin people had shown they wanted the farmers growing some of their produce in developing countries to have a "decent standard of living".
