Chappie this might be of use, it is a clause in the contract that the widows had to sign in the aftermath of the crash;
I was given a summary of the Armed Forces Family Pensions (AFPS). In paragraph 6 it reads
REDUCTION IN ATTRIBUTABLE FORCES FAMILY PENSION ENTITLEMENT
If you have been awarded an Attributable Family Pension, this may be subject to a reduction if at any time you receive compensation from a third party as a consequence of the death of your spouse. If you have received, or receive at a future date such compensation, you should report the full details to the pension authority.
The legality of getting a grieving widow to sign a document without any legal advice is highly doubtful. But this is the sort of trick that the MoD plays in the teeth of human tragedy. Ask Tim Collins if he condones this kind of thing or whether it happened when he was a CO.