Technically, you do not need a MA in translation specifically to work as a translator in the UK (if that is where you want to work). A former housemate of mine currently works as one, he did a MA in French and German (- he's English). He got the job straight away, but was asked to start learning a third foreign language. That is, his fourth language in all.
It bothers me to say but I think that with only one foreign language, you may struggle bad to get a job as translator. Epecially as competition must be fierce for Spanish. For the MA, I believe you may have to have at least two foreign languages and some background in linguistics... Then I just assume it is so! Probably you should check a few universities entry requirements and all, and also job ads, simply enough. Hopefully you'll prove me all wrong!
Good luck anyway :)