Which option should I choose, the BEng or MEng?
This really depends on whether you are aiming for a career as a professional engineer. If you are, you will need the equivalent of an approved (accredited) MEng degree. To be a professional engineer you will need to obtain chartered engineer status and you gain this through having full membership of an appropriate professional institution, (e.g. the Institution of Civil Engineers, the Institution of Structural Engineers or the Chartered Institute of Water and Environmental Management.