(Corrects detail of size of share sale) July 22 (Reuters) - Britain’s government said on Thursday that it is launching a plan to sell down shares in Natwest over a 12 month window. The government said it had instructed Morgan Stanley to sell shares on its behalf starting from August 12, and running until August 11, 2022. It will sell up to 15% of the total volume of Natwest shares traded in the market over the 12-month duration of the plan. The government currently holds a 54.7% stake in NatWest. (Reporting by Rachel Armstrong, editing by Karin Strohecker) Our Standards: The Thomson Reuters Trust Principles.