"I won't forget my conversation with Prime Minister Modi congratulating him on his victory. I picked up the phone and said, 'It's great to be talking to someone who just got more votes than any other politician anywhere in the universe'," he said.
Cameron disclosed his private conversation with India's newly elected leader during an address to Britain's Indian community at an annual event hosted by the Conservative Friends of India here.
"Britain and India now both have bold reforming governments that believe in free enterprise and progress," he said.
The Conservative Party leader used the forum to canvass for Indian-origin votes in the UK's upcoming general election due in May 2015.
"Elections are won in the heart rather than the head. And actually what is at stake at the next elections are not just the policies and plans but the values that lie behind them," he said.
Cameron revealed this while speaking to the Indian community in London
"That is where I believe British Indians have so much to contribute to this fight that we have in front of us. The values that will help Britain succeed are the values that your communities hold dear," he said.
Invoking Mahatma Gandhi, Cameron said: "As Gandhi said, the best way to find yourself is to lose yourself in the service of others."
Cameron said the India-UK ties was "extremely strong" but "I don't actually think we have yet even scratched the surface of how far this relationship can go."
He outlined three key elements that would help build the relationship further - commitment, respect and ambition.
"I know that with India on the rise, Britain should not for one moment take for granted this relationship. As leader of the Conservative party and as Prime Minister, I have given this relationship real commitment.
"The first overseas visit I made as PM was to India. I have visited India now more times than any country apart from Brussels, where I have to go more often than frankly I would like to," he said, making light of his ongoing clashes over greater political control within the European Union.
This is a relationship that should be based on respect.
Both our countries face a terrible threat from terrorism and we shall always work together and fight this together, Cameron added.
"But also respect for the histories, religions, traditions of our respective countries," he said refering to his visit to Amritsar last year.
"I will never forget my visit to the Golden Temple, one of the most beautiful, serene and moving places I have ever been to. Sometimes during the trials and tribulations of this job, I think of that and wish I could be there again. I am very proud to have been the first serving Prime Minister to make that visit," he said amid wide applause from a large number of British Sikhs.
We should also show respect for each other's past and our shared past, he said.
"I think it's absolutely a brilliant decision that we made this week to have in Parliament Square, alongside statues of Lloyd George and Churchill and Mandela, in time a statue of one of the greatest men of the 21st century - Mahatma Gandhi," Cameron added in reference to the recent announcement in India on a new Gandhi statue for London.
The British PM also listed "three fabulous facts" that proved the relationship between the two countries can get "even stronger."
"Firstly, Indian business is investing more into the UK than the rest of the European Union put together; second, UK is the biggest inward investor into India, so the economic partnership is getting ever greater; and fact number three is that Britain's biggest diplomatic presence anywhere in the world is actually in India," he said.
"I think that is a testament to the scale of opportunity that we see in this absolutely vibrant relationship," he aid.
The Conservative Friends of India (CFI), co-chaired by Indian-origin MP Alok Sharma and businessman Ranjit Baxi, is aimed at building stronger links between the Conservative Party, the British Indian community and India.
The annual event was attended by senior politicians, MPs as well as the Indian High Commissioner to the UK, Ranjan Mathai.