LONDON, Aug 12 (Reuters) - Activist investor Cevian Capital said on Thursday that British insurer Aviva (AV.L) has made a "good start" in returning four billion pounds ($5.54 billion) to shareholders but that more needed to be done. "The at least four billion pounds excess capital return by June 2022 is a good start, but four billion pounds would not be enough to address the overcapitalization and we expect the company to return five billion pounds by the end of next year," said Niko Pakalén, partner at Cevian Capital. ($1 = 0.7222 pounds)