Just had another look at the roll of honour - In the 1911 Census, Ernest was living with his father in Selly Oak, Birmingham - 12 years old. He would have had to have moved back to Northampton to enlist. I`m not aware that he did, so I need to do some more research to see if I can confirm this.
I`m not aware of a "Herbert" in my tree, but It`s an ongoing project so he may come to light somewhere along the line.
p.s. I did try to upload the photo of Thomas senior for you, but it won`t load for some reason - is there a limit to the no. of uploads I can make?