It depends on what your mitigating circumstances are, and how understanding your lectures/course leaders are. Have you talked to any on your lecturers, and kept them updated on whats going on with you? I was having an extremely difficult time during my 3rd yr due to medical reasons and let my lecturers know. They were extremely helpful and suggested I freeze my studies and pick up from where I left of once I recovered. It also depends on what your work was like before this, I think my lecturers were more understanding because they knew I was capable of and usually work to a high standard (going by 1st & 2nd yr results). If your mitigating circumstances are strong enough they'll probably let you redo the yr. If not you may be kicked out. But again it just depends I know two people who faild their 1st yrs one was kicked out and the other was allowed to redo the yr. Engineering is a pretty competitive course at Brunel though. I would suggest talking to your tutor, head of course, or one of your lecturers at least it will give you a better idea of where you stand, and hopefully peace of mind.