I don't know if the monarchy pays IHT, or if charities would be included (RNLI etc?) but this recent consultation from HMRC provides an interesting reference. If this is wealth preservation at its most imaginative, then I doff my cap.
https://www.gov.uk/government/upload...doc_vFinal.pdf
The Government wishes to extend the Inheritance Tax exemption for armed forces personnel who die on active service to all emergency service personnel who die in the line of duty, or whose death is hastened by injury incurred in the line of duty.
Having said that, HMRC is about to consult on a pre-loaded HMRC measure though, pay before you die. Oh, the joy.