FRANKFURT, Sept 22 (Reuters) - European Central Bank policymaker Madis Muller played down on Wednesday the prospect of an increase in the ECB’s regular Asset Purchase Programme, saying it wasn’t necessarily “the best way” to keep markets running smoothly. “We should openly discuss all options,” Muller said on Twitter. “But given the currently very favourable financing conditions and the solid recovery, I am not sure if increasing the volume of APP purchases in the spring is the best way to avoid a cliff effect.” He was clarifying his thoughts after Bloomberg quoted him as saying an increase to APP would be part of the discussion.