motor tax is recoverable as long as the car is certified as crushed, a reputable breaker will do this for you.
The insurance can be a bit more complex. If the policy is in it's first year, there may be penalty charges which would wipe out the rebate. If a claim was made resulting in the car being written off, then the policy can be deemed to be used up and a fresh proposal form required to take out a new policy next time round. not many companies now reuire this, but it was common years ago.
If a claim was made rsulting in the car being written off, then the company may say no to a rebate. however, an argument can be made for a rebate of the Third Party element of the premium as there is no limit to that part of the policy.
You can only try, and the worst they can say is NO