By Stefano Rebaudo (Reuters) -Sterling fell against the dollar on Friday as an unfavourable macroeconomic backdrop overshadowed concerns about politics after Prime Minister Boris Johnson announced his resignation. Britain’s government will focus on delivering pre-agreed policy rather than unpicking previously agreed decisions, a spokesperson for Boris Johnson said on Friday. The Financial Times, citing lawmakers with knowledge of the plans, said the Conservative party intended to have a new prime minister in place by the time parliament returns from its summer break in early September. “Johnso…