He occasionally lectured at the School of Oriental and African Studies, University of London, particularly on Persian poetry.
[1] He spoke Persian with a poetic fluency, and additionally could talk in Arabic, Pushtu, Urdu and Swahili.
[3] Historian William Dalrymple dedicated his book White Mughals to Wannell for the latter's help with translation of source texts in Persian and for providing insight with deep knowledge of the Muslim world.
[5] Hugh Thomson writing in his obituary of Wannell for The Spectator compared him to the British literary critic Eric Griffiths.
Dalrymple stated that Wannell's standards were so high that he found it difficult to write anything that matched them and that his output did not reflect his erudition with many commissioned books never seeing the light of day.