Thanks to all for advice.
I rang Hastings Direct Monday. They were helpful, brisk and accepted my claim, said their client was at fault. A woman rang Tuesday, lots of questions, told me an assessor would call Wednesday.
He called this morning, examined the car, took measurements of tread depth, etc. He pointed out that the tow bar was bent sideways, that the rear door aperture was distorted, declared it a write-off.
He asked me what I thought it was worth. I muttered that they appear on e-bay at £2000, that I had to replace the car, that any e-bay car needs collecting, and needs sorting - cam belts, clutches, etc. He smiled. His smart phone had come up with a value of £700, what did I think of that. I hesitated. He asked me what I had paid for it, I replied £400 3 years ago..
I pushed for £800, which he accepted, and said if I wished to keep the wreck they would knock off 10%. It would be a category C wreck, meaning I could not put it back on the road.
Thanks again for your help. I am relieved I have managed it, all in 3 days.