In the UK, you normally need a First Class or Upper Second class grade to be admitted to graduate study.
There is a grade conversion table in para. 4.2 of the Academic Policies (2015) for undergraduates at Jacobs which unfortunately does not include the UK grades.
Most British Universities now give their students both the traditional UK grades (First, Upper Second, Lower Second, ...) and also an ECTS grade (A, B, C, D, ...). Some universities also try to convert one into the other (see http://www.nottingham.ac.uk/courses-office/examinations/ECTS.htm and http://www.kent.ac.uk/studying/short-term/academic.html).
There seems to be a tentative agreement that an a British First Class degree corresponds to approx. the A range of ECTS (Jacobs 1.0 to 1.16) and the British Upper Second range to the B range of ECTS (Jacobs about 1.17 to 1.83). However, the ECTS grades are defined in terms of the percentages of students (with A being the top 10%, B being the next 25%, etc.) so that this may very from one university to another.
In my reference letters I usually state that a first is equivalent to a GPA between 1.00 and 1.67, and an upper second is equivalent to a GPA between 1.68 and 2.33.