Nye & Co. of Bloomfield, NJ, recently had an auction that included this unsigned painting, Lot 39,

http://www.invaluable.com/auction-lot/oil-on-canvas-general-gordon-drummond-DC947D39D2

The plate below the painting is hard to read but it says,”General Sir Gordon Drummond, G.C.B. D. 1854 / Robert McInnes, British / 1801-1886″

There is a short biography of General Drummond in “A Military History of Perthshire / 1660-1902” edited by the Marchioness of Tullibardine, pp. 486-492,

https://books.google.com/books?id=fyE7AQAAMAAJ&pg=PR22&dq=general+gordon+drummond+portrait+agricola&hl=en&sa=X&ved=0ahUKEwinwYzWzPTTAhVqjFQKHQPmD44Q6AEIJzAA#v=onepage&q=general%20gordon%20drummond%20portrait%20agricola&f=false

After page 486 is a reproduction of this painting:

But the painting is listed as not by Robert McInnes but by Filippe (Filippo) Agricola, 1776-1857,[https://en.wikipedia.org/wiki/Filippo_Agricola].  Agricola worked mainly in Rome and usually painted religious pictures.  After General Drummond retired from the British army in 1816, he would often visit Italy so it must have been on one of these trips that he met the artist.

General Drummond’s daughter married the 2nd earl of Effingham in whose family it descended.  It is possible, though, that McInnes made this copy of the Agricola painting and the original is still in the Effingham family.  The book reproduction of the Agricola painting is not very good so as to make a close comparison difficult.