The Civil Service "supports the government of the day in developing and implementing its policies, and in delivering public services." The core values are Integrity, Honesty, Objectivity and Impartiality.
I think it would be fair for civil servants to contribute to Interactive Democracy while applying these core values to the way they conduct themselves in debates and how they support the government as it implements policy. I don't see a problem with them declaring their employment position, or a conflict between their sworn support for the government and their democratic rights. But I can imagine, given human nature, that to avoid conflict in the work place, they may want to remain anonymous.