By Iain Withers LONDON (Reuters) – Standard Chartered Chief Executive Bill Winters said the merits of a UK-based, Asia-focused bank remain valid in the face of “unpredictable” geopolitical tensions. Speaking to Reuters on the sidelines of StanChart’s annual general meeting, Winters said there was a role to be played by banks like StanChart and its larger UK-listed rival HSBC, which is facing fresh calls from its top investor to break itself up. “We are demonstrating that we’re going to make this model work. It has worked in the past,” Winters said. “I can only speak to us but it works for us t…