Sham Consultancy
Your consultant says he is doing much the same job, in the same location and he wants the protection of a long term guarantee. So effectively in his eyes, he has still not changed his employment status - irrespective of the remuneration agreement. Resign on Friday and consult back on Monday. In the UK this practice is well recognised by the Revenue as a tax dodge and they have enacted suitably punitive legislation.
So I would guess that the company is protecting itself, basically saying '...well this guy left and we had a skills gap so we advertised his job. In the meantime we all agreed that he could help cover that gap. We can prove this is only a short term arrangement from our point of view???.
My advice is to 1- Forget that you ever produced an Employment vs Consultancy comparison, and don???t ever refer to this in the office or you will find that your engagement is very short term. 2- Start looking for a new client PDQ. Network as much as possible (and even advertise) to prove that you really are a consultant and are willing to take on the risk and responsibilities of that role. If your only client is your old employer, you wont be consulting for long.