The audience loved the exchange and Cameron, 40, must have known that he had charmed his listeners.
Addressing guests of the Bombay Chamber of Commerce -- which included the reclusive Ratan Tata -- it was Cameron's first major address outside the United Kingdom.
Accompanied by Shadow Chancellor George Osborne -- who is just 35 -- the duo represented a striking contrast to the ageing band of Indian politicians. Especially when British Prime Minister Tony Blair who is supposed to be at the end of his political career is only 53!
On a four-day visit to India, Cameron was in Mumbai on Tuesday after visiting Pune. He will meet Prime Minister Manmohan Singh in New Delhi on Wednesday.
But it wasn't his earlier meetings with Ratan Tata, whose Tata Consultancy Services is the biggest Indian investor in the UK, and Reliance Chairman Mukesh Ambani that Cameron started his speech with.
He began on a somber note, expressing sadness over the road accident that had taken place that afternoon when a British high commission van carrying his aides and some journalists hit a woman in central Mumbai.
As the lady lies critical in hospital Cameron said he was praying she would be okay. The British high commission, he said, would do everything to ensure that she received the best treatment and they would cooperate with the police.
The MP from Witney, Oxfordshire -- who became the second-youngest leader of the Conservative party last December -- has been blogging about his India trip since he left London's Heathrow airport.
Expanding on his thoughts from his India blog, Cameron spoke about the need for forging a new special relationship with India, to meet shared challenges between the countries like terrorism.
Responding to a rediff.com question on how both countries could fortify themselves against the perpetual threat of terror, sometimes from its own citizens, Cameron said:
"I think there are lots of things we do already in terms of sharing intelligence. As you say, sometimes the threat can come from our own citizens, I think that shows the need not just for a security response based on policing and intelligence but also making sure that both India and Britain continue to be successful plural societies, that we build a cohesive society. We make people feel included, whether it is the new India or the new Britain. That people don't feel marginalised. There are both security issues and community cohesive issues that we can work together on."
Educated at Eton and Oxford where he received a BA in philosophy, politics and economics, Britain's Opposition leader was asked:
Whether Muslims were being marginalised in the present scenario
He said all political leaders in Britain have said that Islamic terrorists are completely unrepresentative of the Muslim community and those who follow Islam in Britain.
"The overwhelming majority of Muslims in Britain want to be part of a successful Britain. They believe Islam is a religion of peace and it is very important the political leaders make that point over and over again. When you have a successful multi-racial country like Britain, it is very important that different races don't live in different boxes never interacting with each other. I think there is sometime a danger in some parts of Britain that that has happened and I have made a number of suggestions on how we can bring people together."
"I think in India you have been successful
Making the case for a more open economy
India should continue to take further steps because the upside is huge, he said. India received just half per cent of British overseas investment and less than one per cent of its exports.
"Britain believes that the liberalisation of the Indian economy has been a great success and if it goes further and includes some of the sectors like banking, insurance, legal services, retail that would be good for both countries."
He was sceptical about proactive trade ministers "leaping into airplanes packed with businessmen flying into different countries. I think that was youthful cynicism if I can put it that way. There is a need for a more purposeful aggressive and enthusiastic trading support policy. We need a trade system, a minister who really puts effort year after year towards the great new economies in India, China and Brazil."
The Doha Round
Stressing on the need to restart the Doha Round, he said if there was no breakthrough, a possibility of an EU-India free trade agreement should be considered.
"One of our frustration as opposition is that we can only talk about it and I think every country is going to do all it can to get it started again and Britain's responsibility to push for reduction in agricultural subsidies in Europe and that's the key role we can play. Fortunately in Britain there's quite a consensus behind that."
On his meeting with Prime Minister Manmohan Singh
"It is a listening and learning visit," Cameron said. "About a shadow ministerial team understanding the big challenges that face modern India and making sure that we are an effective Opposition ready for government if we win the election."
His take on society
"A strong society is an essential counterpart to an open economy. A strong society is built on strong institutions.
A company is not just a set of employment contracts.
A community is not just a place where people happen to live.
A nation is not just a hotel.
These institutions support human ties that make life worthwhile. Unless we sustain and strengthen those ties, globalisation will make us economically rich but socially poor."
Would he change the high fee structure for Indian students at British universities if he became prime minister?
"They always say the last question you take is the one you wish you hadn't!"
"The university fee is a very difficult question and subject for British politicians. Britain has a very good higher education institutions and our ability to produce great graduates is very impressive. We've got to build on that, which maybe makes it a very tough decision -- and politically speaking I am not answering that question directly!"
Why India?
"We attach the highest importance to Britain's relationship with India. I want us to develop a special new relationship, that's why I wanted to come here for my first major overseas visit as Leader of the Opposition."
"India is the third largest investor in Britain. 500 Indian companies are based in London. 1.3 million people of Indian origin live in Britain and make an enormous contribution, both economically and culturally. They even contribute to our cricket team!"
And then came Humphrey Bogart...
Cameron chose the famous last lines from Casablanca to describe the new relationship with India: 'This could be the start of a beautiful friendship'.