Had exactly this with a none Motability car. My car at the time was a high end car, they knew I’d be entitled to an equivalent replacement and were desperate to keep the costs down by getting it done quickly. They repaired it and I had it back within 2 days.
My guess is the insurers are worried the claim could be high with replacement car costs if Direct Line can’t get it repaired as quick as they can. Also, when they see Motability they know they could be liable for extra costs related to keeping a disabled person mobile. I’d take the offer as your car will probably be repaired quicker and you have 200 notes in your back pocket.
Enyaq EV