Section 21 and baliffs?

I think you need to go back to the housing officer and check their rules again a Section 21 should be sufficient. It is unreasonable for them to wait until the bailiffs letter to provide you with a new bond, as you will be getting the old bond back when you move. If they are not prepared to move on this you could try a loan from the benefits agency social fund, to cover the period between putting a deposit on a new place and receiving the deposit on the old place. Also try the local CAB, if you still have one.