Britain, as the world's greatest imperial power in the 1860s, would have had plenty of reasons to prefer that the USA be split into two separate nations, as this would considerably weaken the USA as a future imperial rival to Great Britain.

That's realpolitik. It's not at all surprising that the British would have hoped for a Confederate victory and would have given the CSA some covert assistance and helped them out with trade.

A CSA victory would have resulted in a weaker USA and a CSA whose military plans would necessarily be mostly focused on each other in the future rather than overseas. This could only be beneficial to the various European powers (and eventually to the Japanese as well).

A USA victory, on the other hand, would result in a reunited America which would soon become a very serious rival to all the other great imperial powers in the world...and possibly end up stronger than any of them. That's what has happened since the end of the 1800s.

So the British had vital reasons, in a strategic sense, to want the South to win that war...quite aside from the moral issues such as the slavery question.

When it comes right down to it, empires are least moved by moral issues...they are most moved by financial issues and issues of relative military power and positioning.

Why would anyone be surprised that the UK hoped for a Southern win in the American Civil War? A divided rival is a weakened rival...and you can keep on playing one side against the other to your own advantage.

That's just smart imperial strategy.