Shani,
Thanks for your reply. I'm from Argentina. My question stems more from an interest in avoiding having to go through things I have already covered in my previous studies, and really further my knowledge in the field, rather than in finding a formal equivalence.
As you pointed out most courses seem to be taught, with very little research involved - in fact I haven't seen any MRes for my branch of engineering.
From your answer I also draw that an Euroupean MSc more similar to an American (I mean USA) M.Eng., and the American M.S. is more like an MRes - I decided to switch the discussion to the American degrees as I'm more familiar with those than the European ones, and they are likely to be more widely known by everyone else too.

Dear Forum,
I'm considering getting a degree here in the UK, but I'm confused. In my country is quite simple, you get a degree as "Engineer", that would allow you to continue towards a "Master" or a "Doctor" degree. Here you have BS, then MSc / MPhil / ???, and then PhD.
I understand the basic equivalence between the lowest degree (BSc / Engineer) and the highest degree (Doctor / PhD). I'm confused about the degrees in between because of the different possibilities and the differences in the base level (an engineering degree in my country takes 5 years). Also, it seems to me the way masters are approached here is different, i.e., I cannot find the distinction between a master done by somebody already specialized in the field, and a master open to people from other backgrounds (what I would call a post-graduate specialization) ... I have not been able to find a general explanation on the web, and each uni describes their degrees their own way.
Does anybody know a website where I can read about this? Can anybody comment on the subject? Thanks in advance!