TonyE - In trying to condense the material I have on the 9.8 Colt, much of the story was left out. In fact, I probably over-stated one cause for the lack of market success for the 9.8 mm. More on that in a minute.
Tony, your 9.8 mm cartridge could, have course, simply been acquired in trade by a British collector from an American and ended up eventually where you got it. It would be much more fun to assume that it came there in Late 1911 with Reising! Actually, the English Pistol Trials at Enfield in late September of 1911 were the first stop for Charles L. F. Robinson, Vice President of Colt and responsible for Colt’s effort to halt a marketing war with FN, and Eugene Reising, on their European trip that took them to Romania, Serbia, Bulgaria, etc. Along with one of the down-sized 9.8s, they had a "Model of 1911 Special Army .45 Pistol, serial number 10, with them, probably for those trials. You may want to start your research there, and I surely would love copies of anything you find. I will quote an article from the June 1988 issue of American Rifleman magazine, “Colt’s Baby Model 1911,” by William H. D. Goddard, pages 26-29:
"On Oct. 19, Chiarman Skinner read a cable from Robinson for Colt's board. It told first of the Colt's successes in London and Bucharest, and second, gave mention of the specifics of a proposed new FN non-competition contract whereby the Belgians would "withdraw from Mexico and Central America if Colt would keep out of the Balkan States.""
This quote goes to the heart of your question - Reising and his “Baby Colt” were in England before going on to Bucharest, and he had a supply of 9.8 mm Colt ammunition with him. A few rounds may have been passed out to “notables” with an interest in it, as souvenirs, if for no other reasons. More fun to think of your round actually being one coming from the hand of Mr. Eugene Reising.
At the same time, it makes my statements regarding the bellicose situation in Europe having some effect on the sales of Colt’s new pistol, while a possiblity, a weak one at that and secondary to the long-ongoing competative conflicts between Fabrique Nationale d’Armes de Guerre, Herstal, and the Colt Patent Firearms Manufacturing Company of Hartford, primarily concerning the work of John Browning. That story is too long to tell here, but probably the agreement referred to was much more important than the looming conflict in Europe. in the Colts Pistol not being adopted in Romania, where it did very well in the trials. In trying to condense material for my answer, which Lord knows are often too long to the point of boredom anyway, I did not mention the trade in-fighting between Colt and FN and over-stated the situation in Europe as a cause of the Colt going nowhere.
Also, in revisiting my files and putting some facts together, I have found mention of 9.8 mm pistols from serial number 0 to serial number 3, inclusive. Within that numerical grouping, all numbers were found mentioned in one context or another.The whereabouts of all four are not known today. One is known in the collection of the Springfield Armory National Historical Site, apparently a pistol assembled from parts and possibly the one that was in the Kirby collection, in Texas. Serial Number 3 is also known, but I don’t know where it is today. Further, in my mention of one gun returning to the scene being sent to a French trials in 1922, I found in more closely examining the material I have at hand, a conflict in that information. The gun going to the French trials was an FN pistol, while The American Rifleman article by Goddard indicates that in 1922, Pistol No. 2 was booked out of the Model Room to H. S. Campbell, one of Colt’s South American Salesman. Whether he took it for his own reasons, for showing in his normal Hispanic territory, or actually took it to France for a trials, I cannot answer. It is obvious, and should have been to me, that this is a Colt pistol, and has nothing at all to do with the French trials.
Sorry if I muddied the waters in my attempts at brevity in my initial answer. With many of these subjects, there seems always more than one story to tell, and sometimes in making a fairly quick answer, I read my files only as “deep” as it requires to give a response. A bad habit on my part, but necessary to time constraints.
Edited for spelling correction only.