If anybody is still interested in the thread, I believe Twinjet would be prepared to pay in the region of £68,000 pa for a 604 Captain. I do not know who owns the aircraft but as is their way, it will probably do a lot of ad hoc charter work at short notice. Seems they are becoming increasingly desperate as they now state their willingness to type rate.
I have heard mixed reports as to what they are like to work for but mostly not positive.
They apparently used to operate a Challenger that belonged to P&O (a shipping company!!)