You can get full funding for
part time STEM courses (including engineering) from SFE. So if you pursue a part time course (which is not uncommon for engineering courses) you can be fully funded. This would also allow you to work alongside the course, possibly in a related capacity or possibly not (but would at least help support yourself financially). As an alternative to that, you can do a degree apprenticeship in engineering; these are reasonably common, including in civil engineering. You would earn (admittedly, probably a lot less than you do now) while you're working and getting the degree, and you'd be working directly in the industry. There is also always the option of doing a full time course, but you would need to
completely self fund this (tuition fees and living costs; bearing in mind tuition fees are £9250 per year currently, rising in line with inflation)
Most universities will expect you to have undertaken some recent academic study to prepare for the course. I'd suggest contacting universities to see what options there are, but probably the best options would be either an Access to HE course or OU study. You should check with them which Access courses (if any) they accept and/or which OU modules would be appropriate. Importantly, make sure any Access course satisfies their requirements for mathematics background, as this seems to vary a lot for them; OU modules are probably a more straightforward route for most courses, but as always, check with the providers.
Alternately you could take A-level exams again, self studying or doing a distance learning tuition course (or with local tutors); some degree courses however may expect the science endorsement (practicals) for any science A-levels you take (in the newest sitting that is), and this is both expensive and hard to find, compared to just sitting the exams as an external candidate.
You can get an Advanced Learner Loan for an Access course (which will be written off if you complete a degree subsequently) and A-levels, although there is a maximum for this (which I don't know unfortunately). You can be funded for OU under the part time arrangements above; do note however, this second degree funding will likely follow the same format of length of degree plus one year's worth of funding, so I would suggest not taking more than 120 credits with the OU without verifying you can transfer into a higher year of a relevant course. Many courses would expect two level two modules for entry, so check how that works out with the credit amounts and prerequisites etc.
Finally, you could apply to degree programmes including a foundation year - these will cover the relevant A-level equivalent material in a preliminary year and then subject to performance in your final exams, you would progress into the main degree. While these are common for engineering, I don't know how many (if any) will be available for part time courses. This is just basically another year of the degree and you would be funded (or not) by SFE as above for that. Often these do take mature students who have taken A-levels but are some years removed; however, following the golden rule, contact the course providers of any courses being considered to check their requirements in this regard.
Work experience isn't necessary to apply for an engineering course, although might be valuable for you to confirm your interest in working in the area. However, I would recommend focusing on going over the above options to figure out the best route into the course, before spending too much time trying to find work experience. If some comes your way, and you are able to pursue that without financial issues, by all means do so, but don't lose any sleep if you can't, it's really not necessary as far as applying goes.
@Doonesbury @PQ and
@Smack might be able to advise on various aspects as well...?