There are number of contemporary accounts that largely agree with one another and provide sufficient detail to locate the battle and produce a coherent narrative of its course. The relevant extracts from most of the primary sources are reproduced by Stephen Ede-Borrett, Lostwithiel 1644: The Campaign and the Battles, Farnham , 2004, Chapter 8.
Sir Edward Walker, Historical Discourses on Several Occasions, London, 1705: Walker was the King’s Secretary of War and took part in the Lostwithiel Campaign, recording the meetings of the King’s Council of War, which he used in part to write his account of the campaign and battle.
Richard Symonds, Diary of the Marches of the Royal Army, (ed. C E Long), Cambridge, 1997: Symonds served as a trooper in the King’s Lifeguard of Horse in the campaign and had first had experience of the events he described.
Cornwall Record Office, Truro R(S)1/1058, Letter from Sir Ralph Hopton to Prince Rupert circa 25-30 August 1644: Hopton replaced Lord Percy as General of the Ordnance to the Oxford army in mid-August 1644 and was present for the actions around Lostwithiel. His account predates the final stages of the battle and is focused on royalist strategy, though he provides some useful clues as to where the royalists deployed during the attacks of 21 August.
Sir Richard Bulstrode, Memoirs and Reflections Upon the Reign and Government of King Charles I, London , 1721: Adjutant to Lord Wilmot before his dismissal as the King’s General of the Horse in early August 1644, Bulstrode remained with the King’s armies for the remainder of the campaign. His account of the fighting around Lostwithiel is limited, but helps confirm other accounts.
Mercurius Aulicus week ending September 7, 1644: The royalist news book published in Oxford and London provides an account which largely corresponds with other royalist sources, but does provide additional details not found elsewhere. The account is said to have been sent by ‘an Expresse from His majesty’s Army’ and must have been written by an officer serving in Cornwall who witnessed the events around Lostwithiel.
British Library MS Harley 166 f.116, Letter from the Earl of Essex to Sir Philip Stapleton dated 3 September 1644 at Plymouth: Essex’s letter to Stapleton , which also appears in Rushworth’s Historical Collections (The Third Part, Volume the Second, London, 1691 pp.701-703) recounts events from 21 August to 1 September 1644 from the parliamentarian commanders perspective.
John Rushworth, Historical Collections, (The Third Part, Volume the Second), London, 1691, pp.708-711. This provides an attestation from officers within Essex’s army and an account of an examination of Major General Philip Skippon as part of the parliamentary investigation into events in Cornwall. The attestation focuses on the period following the break-out of the parliamentarian horse and, whilst recognising the disaster which befell the army, places no blame on Essex himself. Skippon’s examination blames Colonel Weare and Colonel Boteler for the failure of their regiments to stand in the final action around Castle Dore and provides some details about the fighting there.
British Library, Thomason Tracts E8 The Copie of a Letter from the Lord General His Quarters: Written by a parliamentarian officer serving in Cornwall from Plymouth on 3 September 1644, the letter describes events from 21 August to 1 September 1644.
British Library, Thomason Tracts E10 A True Relation of the Sad Passages between the Two Armies in the West, London 2 October 1644, pp.9-12 provides an account of an officer, EH, serving with the Plymouth Horse which focuses primarily on the fighting on 31 August 1644 during the withdrawal to Fowey.
Stephen Ede-Borrett, Lostwithiel 1644: The Campaign and the Battles, Farnham , 2004 is by far the most detailed and best secondary source on the battle
Richard Holmes, Civil War Battles in Cornwall 1642 to 1646, Stoke on Trent, 1989 is a wider discussion of the fighting in Cornwall in the Civil War, but provides a detailed and solid account of the actions around Lostwithiel.
Mary Coate, Cornwall in the Great Civil War and Interregnum 1642-1660, Truro, 1963 has a short section on Lostwithiel but places the action in the wider context of events in Cornwall during the Civil War.