Cameron wrote to Dr Singh expressing worries about unpredictable Indian government decisions, which could potentially be costly for the two companies.
The British Prime Minister specifically mentioned the delay in government approval for Cairn Energy's 9.6 billion dollars sale of its Indian subsidiary to Vedanta Resources. The deal has been waiting for the nod from Indian authorities for seven months.
The Telegraph reports that the deal has been held up because India's state-owned oil company Oil and Natural Gas Corporation (ONGC), which jointly owns the oil fields with Cairn, wants higher royalties if the deal goes through.
British officials said ONGC's attempt to alter the agreement threatened not only the deal, but also the value of Cairn Energy.
Cameron also referred in the letter to an unexpected two billion dollars demand to Vodafone and unpaid bills of more than 20 million pounds due to British companies who worked on last year's Commonwealth Games staged in Delhi.
The intervention follows Cameron's trade delegation to India last year, on which Sir Bill Gammell, chief executive of Cairn Energy, accompanied him. (ANI)