Is Computer Science a good degree to have?

I mean solely in terms of earning potential

I'd say it's likely to be worse... but not significantly since it is a more practical degree than the others (WRT financial/professional services). CS (and Chemistry) probably have the highest workloads, which means you won't have as much time to take on those positions of responsibility that graduate recruiters love you to write about. I think developing these kinds of soft skills are a big factor for non-technical positions, and they probably come more easily in the traditional engineering degrees.

There's stigma within all of those degrees that going to the financial sector is selling out, but I feel it's especially prevalent within CS.

I get what you are saying, but I mainly wanted to know about the demand and hence pay in the (technical roles in) software engineering/computing, compared to the relevant jobs in the other engineering fields I mentioned.

Although I am not sure if I would like taking Computing as a career choice I'm curious about employment prospects related to CS in the UK and whether it's a good fall back option.

COuld you leaborate on the bit in bold? Surely CS is just as mathematical, and there are ways to take leadership roles etc. as much as in EEE or Mech. Engineering?