AUNG San Suu Kyi has made an impassioned appeal to Britain for help in "the moment of our greatest need" as Burma seeks to build democracy after half a century of military rule.

In a historic address to a joint session of both Houses of Parliament yesterday, the Nobel peace laureate said her country may have to wait decades for another opportunity if it 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.

"There is a process of reform in Burma," he said. "In order for that to succeed we have to work with the regime."

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 is far more difficult than the years before when we had to struggle. We are about to go forward on the most difficult road we have ever walked," she said.

"Now will decide whether we are going to make the breakthrough to democracy."

Her speech received a prolonged standing ovation from the assembled MPs and peers. Commons Speaker John Bercow paid tribute to her "legendary" courage, describing her as "the conscience of her country and a heroine for humanity".

Ms Suu Kyi's visit to Parliament followed a meeting with the Prince of Wales and the Duchess of Cornwall.