Through his research for the biography of Beatty, Leslie became involved in the 'Jutland Controversy', on which he naturally sided with the 'Beattyites' - despite the fact that his naval cousin, Oswald Frewen, whose voluminous but highly entertaining diaries he helped to prepare for publication (‘Sailor's Soliloquy" Ed. G.P. Griggs, Hutchison, 1961), had served under Admiral Jellicoe and was in the opposite camp.

In 1930 Leslie produced 'The Epic of Jutland', about 5,200 lines written in Alexandrine couplets. Stephen Roskill commented "Though it was something of a poetic tour de force some lines in it would certainly have qualified for inclusion in Wyndham Lewis's and Charles Lee's delightful Anthology of Bad Verse, The Stuffed Owl (Dent, 1930) had Leslie’s Epic been produced in time. None the less reviewers generally wrote in kindly vein about it." (original catalogue introduction).