This is a flag of British Burma which was used from 1937 to 1948. I'm just sharing what I found out with no political intention.
Myanmar, formerly named Burma, was under British colony from 1886 to 1948. But Burma (Myanmar) was under British control since 1824 as British began its invasion in 1824, start from coastal territories such as Irrawaddy Delta and Rangoon.
ref : wikipedia.com
Thank you very much.