Of all the many ACW alternates I have read with British intervention none are remotely plausible as they ignore the British personnel on the ground and the officers and troops likely to be assigned.
Was strategy is Sir William Fenwick Williams, Hero of the seige of Kars, Commander in Canada, likely to pursue?
Will Admiral Sir Alexander Milne randomly bombard Union cities? Will he seek to liberate New Orleans? How would a a squadron of the Royal Navy deal with a Monitor - could they even come to blows given their respective drafts?
10,000 to 15,000 British North Americans are in the Union Army - what would they do in the event of war? Of an invasion of Canada?
Is John Fox Burgoyne too old for active service, to march again as his father did on Saratoga (I suspect so)?
What about Robert Napier and the Indian Army? What about Hope Grant's army in China? What about the West Indian Regiments - how would the CSA react to armed negros in America?
Will Britain field its own armies or join with the confederacy? Can the French really get involved given the Mexican Adventure?
What does Britain hope to gain - Maine, Washington Territory, the unguarded Californian coast? CSA goodwill alone?
I have never seen any of this properly addressed in fiction or otherwise...