I struck out on any London baseball games, but two sources on Twain and
baseball did come immediately to mind:

Darryl Brock's MARK TWAIN AND THE GREAT BASEBALL GAME (1999). Issued in a
small edition of 150 copies in wrappers. I don't see any listed online, so
it may be hard to find now.   Includes a vivid account of the 1875 game
attended by Twain and Joe Twichell, with text of the amusing newspaper ad
Twain ran after he lost his umbrella.

Also, Palmer's ATHLETIC SPORTS IN AMERICA (1889), pp. 444-47 which seems to
have the first book printing of Twain's `Welcome Home' speech on baseball (8
April, 1889, at Delmonico's), but with the last paragraph omitted (did he
not actually include the last paragraph when he delivered the speech?). This
printing is not recorded by BAL, Johnson, Tenney [possibly added in a
supplement; I have not checked them all], etc. Anyway, the paragraph gets
added in the text of SPEECHES (1923; the speech was not included in 1910
ed.), and the text given in MT SPEAKING differs as well because it is a
composite based on several sources.

Kevin Mac Donnell
Austin TX