According to an Australian newspaper [The Advertiser, 1 June 1944], he was involved in a frontier incident with Portuguese authorities that could lead to a serious diplomatic problem.
I quote: «The chief press attaché at the British Embassy in Lisbon, Mr. Michael Stewart, has been declared persona non grata by the Portuguese Government and requested to leave.
Mr. Stewart last month was involved in a dispute with Portuguese frontier guards while returning with his wife from a visit to Spain. He allegedly drove over the frontier without a permit when the frontier was closed to ordinary traffic. When he arrived at the next town Portuguese police with machine-gun forced him to halt. He and his Wife were arrested and sent 48 hours in gaol. Eventually it was established that the frontier guards mistook Mr. Stewart for a consular official without the diplomatic privileges which he, in reality had.
They fired on his car as he drove off after an angry exchange. The Portuguese admit their mistake and have apologised for their officials’ impetuosity, but hold that open defiance of their uniformed officials is unpardonable.
The diplomatic correspondent of the Daily Express says that the Portuguese action possesses no diplomatic significance. The Foreign Secretary (Mr. Eden) recognising the fairness of the Portuguese contention, instructed Mr. Stewart to return to London.»