Grigg proved an effective departmental head, but it came as a great shock to many when in February 1942 Churchill dismissed Margesson and replaced him with Grigg – who had to convey the news to Margesson himself. Amongst the many Ministerial appointments made by Churchill from outside the sphere of Westminster politics, this was seen as one of the most unusual, but was a response to considerable military setbacks such as the
fall of Singapore, and the need to appease critics by replacing some ministers. Grigg retained his post for the rest of the war, holding it also in the
Churchill caretaker ministry (May–July 1945). In 1942 he was elected as
Member of Parliament (MP) for
Cardiff East, beating
Fenner Brockway.
Alan Brooke the wartime Army CIGS said that with
PJ he had the "best and most valuable advice on any matter I discussed with him" (unlike Lawson, who replaced Grigg). But in the
1945 general election Grigg lost his seat, and retired from public life. ==Later life==