It's a reasonable request and a reasonable response. Secondment can usually only be agreed if there are funds to pay for someone else to do your job while you're away doing something else. The terms of secondment usually mean that there is a guarantee of some sort that you get your own job back after the period of secondment - so although it's a useful way of gaining wider experience, it's not a permanent promotion opportunity. I would imagine that working for the council, there will be a secondment policy - also (if feel it's worth it) there will be a grievance process for you to protest formally if you think it's not fair. Is there a precedent? - has anyone else been offered secondment?