I'm glad I was able to help yesterday. I agree with you about English File; I think it's a great series.
I've just looked at my copy of English File and the UCLES website. The blurb on the back of the Elementary book says it covers Council of Europe Level A1 and leads into Level A2. According to the UCLES site, the KET exam covers Level A2. So I guess the second book covers the level requird for KET. I suggest you check this with the publisher (OUP); I'm sure they have reps in Spain.
Bear in mind that whilst the book covers the language and skills required for the exam, your students will also need a lot of exam practice and introduction to exam strategies (time management, planning answers.....).