LONDON, Nov 28 (Reuters) - Bank of England Chief Economist Andy Haldane said progress on developing COVID-19 vaccines, combined with huge amounts of stimulus pumped into economies this year, meant inflation could rise by more than expected in the medium term. “As the economic recovery gathers pace next year, it will be important central banks remain squarely focussed on their core medium-term price stability mandates,” Haldane said in a speech to a University College London webinar on Saturday. (Writing by William Schomberg; editing by Sarah Young)