Hi,
Well done on looking into it and I wish you all the best in getting there!
I am a mature student (25) studying engineering at the University of Southampton. I also lacked A-levels due to family situation at the time (I left my sixth form courses). I then worked for a few years until at 21 I decided to pursue education once more.
What I did....
Southampton University offer foundation years for students who do not meet the academic requirements for the main degree programmes for whatever personal reasons. That includes mature students which at over 21 you would be classed as, I was. They still do have a minimum academic requirement, although this can be met with alternatives by mature students, so your apprenticeship, HND or whatever may be sufficient.
I entered into the Science Foundation Year first of all, as for that course, being a mature student, my application was enough to enter without any higher education. The Science Fdn Yr provided equivalence to A-Levels in Biology, Chemistry and AS-Level Math. That allowed me to progress into the Engineering Fdn Yr. The Eng Fdn Yr was much more demanding, hence why I needed further study before entering. For you personally, the HND, etc, may well be enough.
The Foundation years have two main benefits in my mind....
1) Funding the same as any other university course
2) Automatic entry into the main degree programme upon successful completion
I chose Aeronautics and Astronautics, but other friends went into physics, maths, electrical eng, electronic eng, computer science. So it would seem to offer a route to where you want to go.
In terms of the preparation it gave me for my degree, I am in my second year and have so far got a 77.5% average this year. With hard work, the foundation years really are enough.
My advice would be look at what funding may be available to you as coming from an apprenticeship there may be scholarships available from professional engineering bodies. I think IMechE would be a good google. There are also others for the electrical and electronic bodies I'm sure.
Southampton University is ranked highly for engineering and the foundation years have enabled me to get there. My alternative qualifications are not frowned upon by employers. I have just been offered a year long internship with Rolls-Royce and have also been offered an internship with a financial company that I will be taking this summer.
I'm sure other Universiities offer similar courses and your different experiences will be seen as a benefit. More focused, more mature than peers, more settled in life, etc. So good luck to you and any other questions you may have feel free to ask on the thread.
GOOD LUCK!