[Minor edits 12/26/09]
Daniel Morgan, writing 2 days after the battle, described the British deployment at Cowpens as follows:
"The enemy drew up in single line of battle, four hundred yards in front of our advanced corps. The first battalion of the 71st regiment was opposed to our right, the 7th regiment to our left, the infantry of the legion to our centre, the light companies on our flanks."
Banastre Tarleton, writing 6 years after the battle, said that: "The light infantry were then ordered to file to the right till they became equal to the flank of the American front line."
So which view is correct? Were the British light infantry divided into two parts and deployed on the flanks of the British line (Morgan's description), or were they grouped into a single battalion and placed on the right of the British line (Tarleton's description)?
I argued that Morgan's report is more reliable, but histories of the battle that specify the position of the British units have followed Tarleton.
It's understandable that historians would assume that Tarleton is correct. After all, who should know more about the deployment of the British troops than the British commander? Furthermore, there is no reason why he should have felt compelled to misstate the facts in this case (unlike his statements about American troop totals and casualties).
Corroboration or refutation of Tarleton's description might be sought in the Strictures of his critic, Lieutenant Roderick Mackenzie, who served with the 71st lights at the battle. Mackenzie does not correct Tarleton on this count, which may be taken as tacit acceptance of his version. However, this does not necessarily settle the metter. Mackenzie sought to destroy Tarleton's reputation chiefly through logical argument, rather than by offering a different remembrance of events.
David Ramsay's early history of the battle states that at the end of the fighting, "The first battalion of the 71st, and two British light infantry companies, laid down their arms to the American militia." Lawrence Babits' modern history suggests (p 197, n. 102) that the two light infantry companies were the light infantry of the 16th Foot and the Prince of Wales' American Regiment; the 71st lights might not have surrendered with them if they had fled from the right flank to join in an attempted rally of the 71st battalion companies on the left flank.
An alternative possibility is that two of the four companies of light infantry were already on the left flank (as per Morgan's after action report, quoted above) and that these two companies surrendered with the battalion companies of the 71st Foot.
Cornet James Simons of the American cavalry recalled participating in a charge late in the battle "on the right wing of their Army Composed of their Legeonary Infantry, intermixed with the Battallion of the Brave 71st." Because other accounts make clear that the 71st Foot was on the British left, not right, Simons seemingly placed the light infantry of the 71st Foot, at least, on the British right flank.
Copies of Tarleton's and Mackenzie's description of the battle can be found on Marg Baskin's Banastre Tarleton website.
A transcription of Morgan's report and Simons' statement can be found on John Moncure's online history of the battle, The Cowpens Staff Ride and Battlefield Tour.
David Ramsay (1811). The History of the American Revolution (Vol. 2).