It depends on the university and the course. Either way you have to do at least 4 years, but its up to you on the route you want to take... as far as I'm aware.
You are likely to be eligible for CEng with either MEng or a BEng with further learning (i.e. MSc of Engineering). Check the engineering council website for possible courses that interest you to see if they're accredited... this will let you know whether the BEng you're interested in will allow you to be eligible for CEng at a later date with an MSc.
What's putting you off the MEng? I'm sure whichever way you decide to go, you'll be able to transfer between (if the uni offers it) for at least the first year if you change your mind.