British Prime Minister David Cameron has written to Iranian President Hassan Rohani calling for improved ties with Iran, the British PM’s office said."I wanted to write to express the hope that your election will present an opportunity to improve relations between our countries," Cameron wrote in his letter, Downing Street said. On November 27, 2011, a large majority of Iranian MPs voted to downgrade diplomatic ties with Britain. The move was in reaction to Britain's implementation of sanctions on the Central Bank of Iran, over an alleged non-civilian side to Iran’s nuclear energy program. There followed a demonstration in Tehran outside the British embassy during which the UK flag was pulled down. The British government withdrew its diplomatic staff from Iran on November 30 and asked Iran’s diplomatic delegation in London to leave within 48 hours but bilateral ties did not fully severe. Cameron said in his letter to mark the inauguration of Rohani in office that he seeks a step-by-step improvement of relations with Tehran on a reciprocal basis, the Downing Street said. "Improving bilateral relations will be a gradual process and several issues will need to be addressed," he wrote. Cameron’s letter comes as British Foreign Secretary William Hague called his Iranian counterpart Ali Akbar Salehi last week to say London is open to improving ties with Tehran. After the election of the new Iranian President Hassan Rohani, there were calls from the British opposition Labour party, including former British Foreign Minister Jack Straw, for better relations with Iran. However, Iranian Foreign Ministry Spokesman said in response that it is Britain that should move to revive relations with Iran as they unilaterally cut diplomatic ties.