In OTL Britain had favored Spanish control over Cuba, because the possession of Cuba by an unfriendly United States could have harmed British trade in the Caribbean. However, with the guarantee of Cuban independence by the U.S. in 1898, Britain abandoned this policy and supported America's position on Cuba and the war.
What if America had not made this declaration? Would that alone be enough for the British to support the Spanish? If not, what else could have changed the British's position on the war [perhaps much worse/more tense US-UK relations]?
If the British had joined the war on the side of the Spanish, how would this have affected the war? Would it be a Spanish victory? A draw?