I agree with IrishGunner. Compare your photo with the coatee in the centre of the back row of the photo below. My notes, which must have been taken from the auction site from which I downloaded the image, say,
Edit: If you are interested, I now discover that the group was sold as lot 44 for £2,070 in Spink's Sale 1264 on 30 November 2000. The details can be found on Christie's website.
I have just done a Google image search on the photo I uploaded and discover that it has already appeared in a GMIC thread! This may be one of the other discussions about diplomatic dress that IrishGunner mentioned,
http://gmic.co.uk/topic/33016-victorian-diplomatic-uniform-id/
As IG also said, there is at least one other, which I contributed to and which might be worth your while searching for.