It is sometimes confusing to use when as the equivalent of and then.
Will you please forward the necessary evidence . . and an explanation of the reason for delay when the matter will receive immediate attention. (If you will forward . . . the matter will ... )
The certificate should be forwarded to the Local Office at the earliest possible moment when the claim will receive immediate attention. (Please forward the certificate to the Local Office as soon as possible. The claim will then receive. . . .)
I would_ suggest that you complete the attached form of application , when your claim will be fully investigated. (If you will complete. . , your claim will . . .)
Let me have full particulars when I will be able to advise you. (Please let me have full particulars. I shall then be able to advise you.)
Alternatively the Minister may make the order himself when it has the same effect as if it has been made by the Local Authority. (. . . the Minister may make the order himself, and it has the same effect, etc. . . .)