"I am excited by this visit. I am excited by what Prime Minister Modi is doing in India and I'm excited about the partnership that we can build together," Cameron said.
Describing Modi's visit as "extraordinary", Cameron said it was not simply about celebrating the economic ties but "actually building a thoroughly modern partnership between our two great countries".
A brief stop to pay tributes at the Mahatma Gandhi statue in Parliament Square will be followed by speeches at the Houses of Parliament and then at the Guildhall in the financial hub of London.
His talks with Cameron will carry on at the British Prime Minister's country residence of Chequers in Buckinghamshire, where he is being hosted overnight.
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On Friday, Modi returns London for a CEOs round-table which is likely to include representatives from major British companies like Rolls-Royce and Vodafone.
He leaves for Ankara to attend the G20 summit on Saturday after inaugurating a new statue of 12thcentury philosopher Basaveshwara as well as a new Ambedkar memorial in London.
A visit to the Tata Motors' owned Jaguar Land Rover (JLR) factory in Solihull, in the West Midlands region of England, will be the last item on his UK agenda.
Meanwhile, a number of groups have announced a "day of protest" tomorrow, coinciding with Modis visit.
The "Modi Not Welcome" campaign by the Awaaz Network as well as a protest organised by CasteWatchUK will assemble outside Downing Street and then move on to Parliament Square.
"An appropriate policing plan is in place. We are in dialogue with various protest groups to facilitate their requests. No restrictions have been placed on the route," a Metropolitan Police statement said.