I'm no expert on the medals but the red cloak and the maltese cross medallion hidden behind this gentleman's hand are highly suggestive that he is a senior member of the Order of the Bath (Military Division).Sir John Moore
(1761-1810) seems implausible based on this portrait of him held by the UK National Portrait Galleryhttp://www.npg.org.uk/live/search/portrait.asp?search=ss&sText=Sir+John+Moore&LinkID=mp03154&rNo=0&role=sit
. Some of the differences could just be a matter of the ageing process, but in the UKNPG portrait his nose is more regular plus he has brown eyes whereas I think your chap has blue?General Sir Charles James Napier
(1782-1853, 'Conqueror of Sindh') also seems implausible. There are a number of portraits for him, all them showing him as quite hirsute. Check out this collection of portraits http://www.npg.org.uk/live/search/person.asp?LinkID=mp03249
. Admiral Sir Charles John Napier
(1786-1860) looks to be a better match, see http://media-2.web.britannica.com/eb-media/82/38082-004-033004AC.jpg
. You'll note the face is very similar, and the sideburns, dark eyebrows and Order of the Bath medallion are the same. I'm not sure why he'd be wearing a red jacket given his naval background but maybe it was court dress associated with the Order, whose mantle was also red?
Unknownsoldier also mentions John Ramsay
. This could be a number of people - John Ramsay (1775-1842), a Lt-General in Indian Army; John Ramsay (1847-1887), 13th Earl of Dalhousie and naval officer; or Major-General Sir John Ramsay (1856-1920). I am inclined to discount them as I couldn't find any record of them being members of the Order of the Bath. However, I didn't do a comprehensive search nor could I find any decent images of them.
Still within the Ramsay family, another possibility might be General Sir George Ramsay
(1770-1838). He was a senior member of the Order of the Bath, served under Wellington and ended up as Commander-in-Chief of British India. He also had a passing resemblance to our chap based on the few low-res images I've been able to locate of him. (Having said that, Admiral Sir Charles Napier would have a stronger claim based on the images I've reviewed.)
Does this help at all???