Cokayne, G.E. (1959): , red. Geoffrey H. White. XII (Part II). St. Catherine Press. Gibson, J.P.: «A Defence of the proscription of the Yorkists in 1459», , XXVI, s. 512. Griffiths, R.A. (1968): «Local Rivalries and National Politics: The Percies, the Nevilles and the Duke of Exeter 1452-1455», , . Griffiths, R.A. (1981): , London, 2. utg. 2000. Harris, Barbara J. (2002): . Oxford: Oxford University Press. ISBN 0195056205. Harriss, G.L. (2004): «Willoughby, Robert (III), sixth Baron Willoughby (1385–1452)», . Oxford University Press. doi:10.1093/ref:odnb/50229. Macfarlane, K.B. (1945): «Bastard Feudalism», , , s. 161. Myers, A.R. (1953): . Richardson, Douglas (2011): Everingham, Kimball G., red. . (2. utg.). Salt Lake City, ISBN 1449966373, s. 511–513. Richardson, Douglas (2011): Everingham, Kimball G., red. . (2. utg.). Salt Lake City. ISBN 1460992709. Sadler, D.J. (2000): , Bristol. Storey, R.L. (1957): «The Wardens of the Marches of England towards Scotland 1377-1489», , Storey, R.L. (1999): , 2. utg.