As far as can be determined via research & opinions here, The ivory appears to be hippo, but other more expert people would have to make comment on that as I am not an expert at ivory of different types.
The size of the knife in total is 14 inches long, the blade does not appear to have been cut down as was suggested by one guy, although it does have signs of sharpening and appears to be 19thc.
The link below which shows 3 knives very like this knife, even down to the style of the bolsters on them and mine, the pins through the hilt which are silver or nickel on the one I posted initially, and on all 3 of the knives in the pics and link, and the style and designs of the hilts, materials etc, they are very alike other than the gold medallions in thin sheet gold, so much so that I expect this knife is actually from the same region as these 3 knives, I also think this knife would have had gold sheet medallions on it where the red lacquer resin in places in the holes on the hilt now but the gold has at some time been removed (?), seems perfectly logical to me, it would also seem quite logical to think that the knives were not African made as in the link here attached but made for the African tribal people of the region by migrant makers of Islamic origin.
So, the idea is that these knives may well have been used and collected from the Yao minority tribal peoples of this region Tanzania and possibly from other tribal peoples there to, they would likely have been high-end pieces to and well regarded by those native tribal people '' the Yao '' and possibly others, but likely they were made by Muslim Indian or Arab migrant peoples of the region and who distributed them in the region, hence the idea that they are Yao and the few museums that have them in Britain having been collected by British colonials having attributed these knives to the Yao tribal regions and people of the region mentioned here below.
Also, these are not uncommon to UK, they seem to be here in more numbers than anywhere else, which likely would explain the colonial link and trade during 18th and 19thc, it appears perhaps some were higher end than other to but all appear to have certain traits materials and marks that have been used in the making of them.
(The Yao !!!, are various Bantu-speaking peoples inhabiting southernmost Tanzania, the region between the Rovuma and Lugenda rivers in Mozambique, and the southern part of Malaŵi. By 1800 the Yao had become known as traders plying between the inland tribes and the Arabs on the east coast).
https://www.michaelbackmanltd.com/ob...h-gold-enamel/
Quoted from Micheal Backman antiques.
"Ivory and gold work such as this is extremely rare. It is related to the ivory and gold work used on Omani-influenced sword hilts that were manufactured in Zanzibar in the eighteenth century. Examples of these swords are illustrated in Hales (2013, pp. 237-139).
Zanzibar comprises two larger islands and a series of smaller islands 25-50 kilometers off the coast of East Africa. Arab traders visited and traded with the islands for many centuries. In the 16th and 17th centuries, Zanzibar was under Portuguese control. And in 1698, it was sized by the Sultanate of Oman, and a ruling Arab elite with a local sultan was installed which developed the local economy further enhancing its trading links with the Middle East and with India.
Important trading communities of Muscat-descended Arabs and Indian Muslims established themselves in Zanzibar. The Indian Muslims comprised Ismailis – Khojas – and Bohoras particularly. Parsees from India also were another significant community. Another Muslim community, the Wahadimu, evolved too, by intermarriage between Africans and Arabs. Other groups included Ceylonese, Christian Goanese of Portuguese and Indian descent, and Indian Baluchis.
Zanzibar became renown as a source of ivory, spices and slaves. It also became a regional entrepot and was an important source of goods that were traded into Africa. The Sultan of Zanzibar also controlled parts of the East African coast which also facilitated this. By the mid-19th century, Zanzibar was the biggest slave center in East Africa with around 50,000 slaves passing through its docks each year.
By the late 19th century, Zanzibar was under the control of the British. The islands gained independence from Britain in December 1963. A month later, the Republic of Zanzibar and Pemba was formed in a revolution that saw thousands of Arabs and Indians killed. The following April, the republic was subsumed into the mainland former colony of Tanganyika (later Tanzania). Zanzibar today has semi-autonomous status."