By David Milliken and William Schomberg LONDON (Reuters) -The International Monetary Fund (IMF) warned Britain’s Conservative government on Tuesday not to cut taxes in the run-up to a national election expected later this year, due to high levels of public debt and growing demands on services. The warning from the IMF’s chief economist, Pierre-Olivier Gourinchas, came after the body cut its forecast for British economic growth next year as part of a wider forecast update. “We would advise against further discretionary tax cuts,” Gourinchas said in response to a question from a reporter. He hig…