Long-term work plans? Exit the rat-race and aim for true self-employment: PC repair business, photography business for example; whatever I'm destined to do.
I think that is what every NEET or low paid person on the forums seems to rather unimaginatively dream of when considering self employment... along with buying some BTL properties.
Do you not enjoy being a civil engineer then? That is an issue, it generally better to be passionate about something if you want to be really successful at it. I mean why not contract as an engineer, look into setting up an engineering consultancy. It just seems really odd to think about self employment then conclude that repairing PCs is somehow a good option???
I don't think rage quitting your job is a good idea either.
I don't know too much about civil engineering but I think I've got a reasonable understanding of compensation - you seem to feel entitled to better pay because you worked hard for a bit at university, I've got to tell you that it simply doesn't work like that - there are various factors that can affect your pay:
having a skill that is in demand - presumably there are plenty of civil engineers out there else you'd be paid rather more than you are... so perhaps you'll need to specialise in some way, or build up a good reputation or get some seniority and be in a position to not only do your job but be well established/competent and experienced enough to supervise a team of others - this will all be easier if you're passionate about your job
the most highly paid people however have a stake in the business they're involved in - sometimes they don't literally own a stake, it could just be a contractual share of the profits they or their team generate (or even discretionary but working to a general set of unwritten rules) for example sales people entitled to a certain compensation structure based on the revenue they generate, traders in banks/hedge funds. Senior management get stock options as do startup employees, some solicitors are fortunate enough to make it to partner, ditto to accountants and some people set up their own firms. If you want to earn a lot then basically you need a stake in the business - in your case, that would seem to taking on contract engineering work and eventually starting to employ others beneath you to do the same thus starting to build a small consultancy. (you then need more than engineering skills - you need to be a manager, a salesman, an account manager etc...)