Wanted to join in this, seems very similar to the experience my wife is having after an accident in June 2019. Diamond referred her to Auxillis for a "hire car" and all seemed rosy. Now my Wife is apparently taking the other driver and insurance company to court.
We've just had to submit financial statements and pay slips to prove she couldn't have afforded to hire a car herself for the 21 days it took for the repair to be completed. Fortunately, the car was no better than ours (Vauxhall Grandland for our C Max, which felt like a downgrade) but it is unnerving and time consuming, especially as we need to find 6 months of statements from over a year ago.
Also, apparently the court selected is Northampton (we're in Bournemouth so we'll be asking for that to change if possible!!!)