Had an accident a month ago, my car was a write-off, it wasn't my fault. Her insurance company [esure] sent me a letter worded "We enclose a cheque for £xxx.xx as an interim payment in respect of your claim against the policyholder." The amount is less than the car was insured for. Is this how it's done and why or are they trying to fob me off. It just seems like an odd way off doing things.

"interim payment"
Sounds like they are trying to me reasonble by sending you some money so you can get going.
If you at all concerned call you insurance (you've paid them to manage your claim)

If it is an interim payment then that indicates that it is NOT FULL settlement but a payment made to you to make life easier untill full settlement is agreed.

As long as that is the basis of the payment then fine. In one sense at least there is no disputing liability. Dont usually get interim payments unless its for something like a fire damage or flood damage to help the occupier or it involves some kind of injury in a motor accident. If its a straightforward write off then it shouldnt need interim payment. Is there a injury claim tied in? If so this may be the settlement of the vehicle part and then they will deal with the longer process of injury claims.

Oh and unless its some sort of claissic car, cars are not insured for anything other than fair market value.

send or scan & email copy letter to yr insurance co to ask them to ask esure what it is for

write to esure saying something like you've asked your insurer to contact them to clarify details of what the payment is for

couild be considerate but more likely cheeky though wording "interim" suggests is in good faith but not without an explanation

some sort of paper chain may prove useful if you end up in a dispute

mother in laws car written off last week – insurers offer = retail book price (glass's guide) with low mileage/1st class condition adjusted less 5% which compared to some stories i've heard was good and a figure that would actually truly replace the car