LONDON, Oct 27 (Reuters) - Finance minister Rishi Sunak on Wednesday set out the latest iteration of Britain’s fiscal rules, with an aim to reduce public sector debt while ensuring the government borrows only for investment. “Underlying public sector net debt excluding the impact of the Bank of England must, as a percentage of GDP, be falling,” Sunak told parliament in his budget statement. “Second, in normal times the state should only borrow to invest in our future growth and prosperity.” The rules apply over a three-year horizon, Sunak said, adding that the government has already met the rules under the judgement of the Office for Budget Responsibility. (Reporting by Andy Bruce; editing by Costas Pitas)