I recently changed from first year Pharmacy to 2nd year Biomedicine with the hope of doing graduate Medicine... It was difficult to change course, and that was after having done really well in my first year modules. I think you need to really have a think if Uni is for you, because it sounds like you are struggling - Engineering is a very difficult degree, it sounds like you have just made a snap decision to study it because of your uncle. If you do well in your access course then that's a good start, but I think what will worry admissions tutors is that you have a bad history with University, and if they give a place to someone who messes up, then it looks really bad on the Uni and they will obviously want to minimise that at all costs. I think what I am trying to say is, no good University will give you a place because you have screwed up so much in the past - the only institutions who may consider giving you an offer are places like London Met, London South bank Uni, i.e. places near 100 in the league tables. There is no point going to University to study something common like Engineering there, you will simply always be outclassed when going for jobs, which brings me on to my next point. With such a bad history of starting things and not finishing things, you will find it very difficult to get a decent career - even if you have a 2.1, purely because it is the standard for graduates to have a 2.1, which they usually achieved first time without any hiccups - your failed attempts will look so bad for you when competing against sometimes 20 other graduates for a job.
So, although what I posted above might be very difficult for you to accept, and make you frustrated, it is better to be told a realistic opinion early on so you can prepare yourself better and increase your opportunities. What I would suggest to you, is to get about 5-7 years solid work experience - it is all you can really do, and with that experience you will be able to make a decent career for yourself. If you go down the university route, you will waste too much money, end up with a degree from a poor institution, and you will be 5 or 6 years down the line, without any real work experience, when you could have spent that time and saved that money, by working and hopping along the career ladder. There is no shame in not going to uni and getting a degree, you can still be "middle class" if you are concerned about social status.
Good luck in whatever you achieve, but I urge you to be true to yourself and not feel forced into going to uni because it is what everyone else seems to do. Sometimes uni is not the right route for someone.