Lots of universities accept Access course diplomas for engineering, but the 'higher-ranked' ones tend to want you to do a foundation year as part of the course. Personally, I want to (and have applied and received offers for) do a foundation year because I simply don't think that you learn enough of the material in a one year Access course (I feel like it's designed simply to get you the marks to get into uni - it doesn't really explain much of the theory), so I'll feel a lot more comfortable going over the basics again - albeit in more detail this time.
It's up to you, really. Most people on my Access course don't want to do a foundation year because of the extra time and money it will cost, and that's fair enough. There are plenty of universities that accept Access students without wanting them to do a foundation year.