While I agree with you, under normal cirmustances, they wouldnt be, as it would be in the fine print on the quote or sheet given to you, that they will not take responsibility for cars on site, prior to commencement of work. (Many mechanics have the same policy, including Subaru dealerships in regards to cars getting service/work done)

but since Just Cars are dealing with it, then it should be their problem, not yours megs. The problem is just getting the insurance company to agree.

If unsure, there are places to ring to find out exactly what your rights are on this, because thats a load of crap.