Depends on the course, and their requirements - it's certainly possible. It's even possible to get a 2:2 in your subject and remain in it...
You may want to discuss this with your personal tutor/director of studies, and see what their perspectives are - it may even be possible to change to your desired subject area within your current university, at the undergraduate level, without having to "start over". That would of course depend on the course, but I know people who have done it. Equally you may be able to (or have no other recourse but to) finish your degree in engineering, but given you've realised you don't want to pursue engineering as a career, you may be able to switch to a non-accredited "general engineering" type course and have more leeway in your module selection to try and maximise your eventual graduating degree classification.
Ultimately I'd suggest starting with your tutor and/or DoS and go from there, as that is really why they are there, and they are best positioned to give you advice based on all the (academic) information. I would say, do consider whether a subject change is going to make the difference here - as someone that left an engineering degree I can certainly sympathise with your situation, but I certainly think in retrospect just changing subject would not have helped me, as a lot of my "problems" ran deeper than mere dissatisfaction with my subject (although that certainly didn't help). What is the subject you want to go into though?