Myanmar democracy icon, Aung San Suu Kyi delivers an address to both houses of parliament in Westminster Hall
The Nobel Peace Prize laureate said her Southeast Asian homeland had yearned for democracy for decades, and could not afford to waste its chance to build a "truly democratic and just society" after 47 years of military rule.
"I am here, in part, to ask for practical help: help as a friend and an equal," Suu Kyi told around 2,000 lawmakers and guests, who gave her a standing ovation that echoed around parliament's cavernous Westminster Hall, reports AFP.
The Myanmar opposition leader, who was wearing a purple longyi skirt and a white shawl, said it was an "extraordinary honour" to address the 11th-century building, an invitation previously only offered to heads of state.
Since World War II, US President Barack Obama, Pope Benedict XVI, South African president Nelson Mandela and French president Charles de Gaulle are the only other foreigners to have addressed both houses in Westminster Hall.
"We have an opportunity to re-establish true democracy in Burma," said Suu Kyi, using the former official name of Myanmar.
"If we do not use this opportunity -- if we do not get things right this time around -- it may be several decades more before a similar opportunity arises," she warned.
The 67-year-old added: "Our own determination can get us so far; the support of the people of Britain and the peoples around the world can get us so much further."
She urged Britain, Myanmar's former colonial power, to help her country develop its institutions, warning that the parliament she recently joined would "take time to find its feet".
She also encouraged "democracy-friendly investment" in her impoverished homeland, two days after Myanmar President Thein Sein pledged to follow dramatic political changes with economic reforms.
Investment that prioritises "transparency, accountability, workers' rights and environmental stability" would be welcome in resource-rich Myanmar, she said.
But she warned that Myanmar's development was continuing to suffer at the hands of the violence that has gripped parts of the country since independence in 1948, and urged aid for the tens of thousands displaced in recent months.
"In the immediate term we also need humanitarian support for the many people in the north and west -- largely women and children -- who have been forced to flee their homes," she said.
Suu Kyi was freed from nearly two decades of house arrest in November 2010 and became a lawmaker earlier this year as part of a gradual transition towards democracy in Myanmar.