Hailing billions in new business deals between the two countries, Cameron promised to "set this relationship free" from its colonial past. Modi said the visit marked "a huge moment for our two great nations."
Although it's not a state visit — since Modi isn't a head of state — the three-day trip has a lavish level of ceremony. Modi was welcomed by ranks of Scots Guards, saw a ceremonial fly-past by the Royal Air Force Red Arrows aerobatic team and gave a speech to Parliament. He'll also have lunch with Queen Elizabeth II on Friday at Buckingham Palace.
Still, there has been criticism of the star treatment for Modi, a Hindu nationalist who has been accused of failing to stop growing religious intolerance and violence in India, including the lynching of Muslims for allegedly eating beef.
Several hundred people, including Muslims, Sikhs, Nepalis and members of women's groups, protested Thursday outside Cameron's 10 Downing St. office, accusing Modi of overseeing the persecution of India's minorities. Modi was taken into Downing St. through a back route to avoid the protesters.
At a news conference, he insisted that intolerance was unacceptable in the "land of Gandhi."
"We do not tolerate such incidents at all," Modi said. "We take strong actions."
India and Britain have close, complex ties dating back to Britain's time as colonial ruler until the mid-20th century. Nowadays, Britain is eager for more access to India's fast-growing economy and its market of 1.3 billion people.
Cameron said relations between the two countries, once "imprisoned by the past," were now a "modern, dynamic partnership" between the world's fifth-largest economy — Britain — and India, which will soon rank third.
Cameron said the two countries expected to sign 9 billion pounds ($14 billion) worth of commercial deals during Modi's visit, including a plan for London's financial district to become a center of offshore rupee bonds, and U.K. investment in three Indian "smart cities" — part of a plan to bring 21st-century road and telecommunications infrastructure to the vast and underdeveloped country.
"We want to become your No. 1 partner for securing the finance needed for this ambitious plan," Cameron said.
In a speech to both houses of Britain's Parliament, Modi said the destiny of India was "the destiny of one-sixth of humanity."
He said the relationship between Britain and India would be "one of the leading global partnerships."
Following a state visit to Britain last month by Chinese President Xi Jinping, Modi's trip is a sign of the growing economic clout of Asia's fast-growing economies.
Britain is already the largest investor in India among G-20 countries, and Indian firms have also made major investments in Britain, including Tata Motors' ownership of automaker Jaguar Land Rover.
The Confederation of British Industry, a business group, welcomed Modi's visit and praised his "business-friendly approach." But critics said Britain should be wary of the Indian leader's poor human rights record.
More than 200 writers, including novelists Salman Rushdie, Ian McEwan and Val McDermid, signed a letter expressing concern about what they called "a rising climate of fear, growing intolerance and violence towards critical voices" in India.
Modi swept to power in 2014 on promises to develop India's economy and root out the corruption and incompetence that had crippled the previous government. But his BJP party suffered a recent drubbing in an important state election widely seen as a referendum on Modi's popularity. And India's economic growth is slowing, although it still outpaces much of the world.
Modi has not always been welcome in London. Britain and the U.S. both shunned him after 2002 anti-Muslim riots killed at least 1,000 people in India's western state of Gujarat, where Modi was then the top official.
Muslim leaders and human rights groups said Modi did little to stop the violence, a charge he denies. India's Supreme Court has said it found no evidence to prosecute him for the violence.
Modi is to spend Thursday night at Chequers, the U.K. prime minister's official country retreat. On Friday, he'll lunch with the queen before capping his visit with a glitzy rally, complete with fireworks, for thousands of supporters at London's Wembley Stadium.
(AP)
Indian Prime Minister Narendra Modi gestures as he arrives at Heathrow Airport, London, for an official three day visit Thursday Nov. 12, 2015.
Indian Prime Minister Narendra Modi is greeted by Minister of State for the Foreign and Commonwealth Office, Hugo Swire, right, as he arrives at Heathrow Airport, London, for an official three day visit Thursday Nov. 12, 2015.
Indian Prime Minister Narendra Modi gestures as he arrives at Heathrow Airport, London, for an official three day visit Thursday Nov. 12, 2015.
The Union and Indian flags hang near the London landmark Big Ben in Parliament Square in London, Thursday, Nov. 12, 2015. Indian Prime Minister Narendra Modi is in Britain for a three day visit.
The Union and Indian flags hang near the London landmark Big Ben in Parliament Square in London, Thursday, Nov. 12, 2015. Indian Prime Minister Narendra Modi is in Britain for a three day visit.
Indian Prime Minister Narendra Modi is presented with a garland of blossoms in celebration of Hindu new year as he arrives at Heathrow Airport, London, for an official three day visit Thursday Nov. 12, 2015.
Indian Prime Minister Narendra Modi gestures as he arrives at Heathrow Airport, London, for an official three day visit Thursday Nov. 12, 2015.
Indian Prime Minister Narendra Modi, right, talks with British Prime Minister David Cameron after inspecting a military guard of honor on the first day of his three-day visit to Britain at the Treasury in London, Thursday, Nov. 12, 2015.
Prime Minister of India Narendra Modi, left, and British Prime Minister David Cameron leave No. 10 Downing Street in London, Thursday, Nov. 12, 2015. Modi is on a three day visit to Britain.
Protestors against the visit of Indian Prime Minister Narendra Modi shout on Whitehall in London, Thursday, Nov. 12, 2015. Indian Prime Minister Narendra Modi is in Britain for a three day visit.
Protestors against the visit of Indian Prime Minister Narendra Modi shout on Whitehall in London, Thursday, Nov. 12, 2015. Indian Prime Minister Narendra Modi is in Britain for a three day visit.
India's Prime Minister Narendra Modi, attends a meeting with Britain's Prime Minister David Cameron inside 10 Downing Street, in London, Thursday Nov. 12, 2015. Modi is on a three day visit to Britain.
India's Prime Minister Narendra Modi, left, shakes hands with British Prime Minister David Cameron after a joint press at the Foreign Office in London on Thursday Nov. 12, 2015. India's Prime Minister Narendra Modi will meet Britain's Queen Elizabeth II and address a huge rally at London's Wembley Stadium during a three-day visit to Britain.
India's Prime Minister Narendra Modi pays homage at the statue of Mahatma Gandhi, in Parliament Square, London, Thursday Nov. 12, 2015. Modi is being treated to full British pomp on his busy three day trip that comes amid rising troubles for him at home, where economic growth is slowing and political criticism is growing.
Britain's Prime Minister David Cameron and India's Prime Minister Narendra Modi, right, leave together after paying homage at the statue of Mahatma Gandhi, in Parliament Square, London, Thursday Nov. 12, 2015. Modi is being treated to full British pomp on his busy three day trip that comes amid rising troubles for him at home, where economic growth is slowing and political criticism is growing.