It depends on a variety of things - not least the following:
1) Grade
2) Experience
3) Department
4) Place of work
5) Qualifications
6) Specialisation
For "just out of university fast streamers" you're looking at £22,000 starting (depending on department - Treasury and FCO can get away with lower as they are prestigious) rising to around £32,000 after your 4th year and £40,000+ on promotion from the Fast Stream to team leader/Grade 7 level.
PR