MEng 4 years - undergraduate degree only
BEng 3 years + MSc 1 year - undergraduate and postgraduate degree
The MEng was introduced in the late 80s/early 90s and isn't a Masters degree, a Masters degree is a postgraduate qualification, i.e. you have to already have an undergraduate degree.
You should find the MSc more stimulating than your undergraduate course for various reasons:
- there's a lot to cram in
- the people genuinely want to be there
- when you finish you'll have 2 degrees and have a postgraduate qualification
- you will have completed a real research project