Well, the Maull and Co. Mark dates it to 1873-1878, Henry Maull was known for his portraits of Parliament members and other noted individuals, but all of his works that I can find are photographic. So I'm not sure if that would be a photo of a painting, or possibly even a photo that was later painted over, it would really need to be examined in person by an expert to determine what it is for sure. Unfortunately as I can't find any similar works I am unable to give you any idea who the person depicted is, or any idea of the value...
Re: 19th century painting
Well, the Maull and Co. Mark dates it to 1873-1878, Henry Maull was known for his portraits of Parliament members and other noted individuals, but all of his works that I can find are photographic. So I'm not sure if that would be a photo of a painting, or possibly even a photo that was later painted over, it would really need to be examined in person by an expert to determine what it is for sure. Unfortunately as I can't find any similar works I am unable to give you any idea who the person depicted is, or any idea of the value...