Aung San Suu Kyi has made an impassioned appeal to Britain for help in "the moment of our greatest need" as Burma sought to build democracy after half a century of military rule.
In a historic address to a joint session of both Houses of Parliament, the Nobel peace laureate said her country may have to wait decades for another opportunity if they failed to seize the chance for reform.
She said she was seeking practical assistance from the UK "as a friend and equal" to overhaul the education system and inject "democracy-friendly" investment into the country.
Earlier, following talks in No 10, David Cameron said Britain was ready to invest money and people - including sending a delegation of MPs and peers to "scope" the potential for reform.
The UK would also be investing £3 million in peace-building work to address ongoing violence in Burma, and increase support each year for education, healthcare, business and the rule of law.
The Prime Minister confirmed he had invited Burmese President Thein Sein to visit Britain, saying he believed he was "sincere" in his commitment to reform. Mr Cameron said he wanted to build on the dialogue they began when he visited Burma in April following Mr Sein's decision to allow Ms Suu Kyi's opposition National League for Democracy to stand in parliamentary elections.
He described the appearance of Ms Suu Kyi in Downing Street - after 24 years in which she could not leave her country for fear she would not be allowed to return - as "a great moment that few expected and few dared to hope for".
In their joint press conference, Ms Suu Kyi described the transition to democracy as "the most difficult bit" and urged countries like Britain to act as "watchdogs" to ensure there was no slipping back to dictatorship.
It was a theme she continued when she delivered her address to a packed Westminster Hall, saying the Burmese people had had to wait decades for an opportunity to establish true democracy. "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 again," she said.
She said she hoped they could draw on Britain's long experience to establish a stable parliamentary democracy of their own. "I am here in part to ask for practical help, help as a friend and an equal, in support of the reforms which can bring better lives, greater opportunities to the people of Burma who have been for so long deprived of their rights and their place in the world," she said.