Amelia and Charlie's consent

The letter signed by Amelia and Charlie Martin, giving consent to their son James Martin joining the expeditionary force. "If you let me go I'll write to you and stay in touch. But if you don't I'll run away, join under another name, and you won't hear from me again." It was emotional blackmail – and we can understand why they signed the letter. At the time, no birth certificate was required: just a letter, and they're easily forged. Jim could have done it.