Indonesia and accused Britain of putting commercial interests ahead of human rights on Wednesday on the first day of a state visit by the Indonesian president.
President Susilo Bambang Yudhoyono received a lavish royal welcome for the first Indonesian state visit to Britain in more than 30 years, but activists criticised the British government for valuing commercial ties over the rights of Indonesian minorities.
Indonesia has one of the world's fastest growing economies and is seen as one of the most democratic countries in Southeast Asia, but its military has kept a tight rein on Papua, home to a mine with the world's largest gold reserves.
Indonesia's government and military have been criticised in the past for human rights abuses in West Papua, after Indonesia took over the province in 1969 in a vote by community leaders that was widely criticised as flawed.
A low-level insurgency for independence has simmered on Indonesia's eastern-most island for decades.
Protesters, some wearing Halloween masks and ghoulish face paint, gathered outside the prime minister's office on Downing Street and waved red paint-splattered placards calling for the release of Papuan political prisoners, imprisoned for advocating independence from Indonesia.
Others, including representatives from Amnesty International and Indonesian non-government organisations, waved West Papuan flags, an act they said is punishable by 15 years in prison in Indonesia.
"It's disgusting that one can walk up towards the Palace and the Indonesian flag is flown on behalf of our government supporting the like of Indonesia," protester Bob Corn said.
Nearby, the Queen greeted President Yudhoyono and his wife in a red-carpeted pavilion on Horse Guards Parade, as a 41-gun salute rang out and regimental bands in bearskin hats played the Indonesian national anthem.
Britain is keen to foster a strong commercial relationship with the fast-emerging nation and has channelled resources from its embassies in the European Union to boost its diplomatic presence in Indonesia and the region.
After the official welcome, Yudhoyono was whisked off in a gilded carriage to Buckingham Palace for a private lunch with the queen. In the three-day official visit, Javanese-born Yudhoyono will attend a state banquet, address parliament and open the Indonesia-UK Business Forum.
(Corrects to describe Bob Corn, quoted in story, as a protester)
(Reporting By Alessandra Prentice; Editing by Michael Roddy and Myra MacDonald)