Historical evidence supports this. In a 1939 House of Commons debate, Sir Stafford Cripps said the Government had "poured abuse" on opposition MPs for urging stronger action against Fascist aggression, accusing them of being "warmongers and peace-breakers." A later Guardian report on the same anti-appeasement MPs says they "were attacked as warmongers" for warning Britain about Hitler. So the statement that those MPs were called warmongers is accurate, though it was a political slur rather than an official title. Sources: UK Parliament Hansard (3 April 1939), The Guardian (4 October 2020).