Hello Vic.
First, did you know that Ancestry now have quite a few images of the 1911 census for London on their site. I have loads, both on my Father's and Mother's sides of the family. Shortly I will be spending a morning in the library just downloading entries. Do you have any that you want? Let me know and I will see if they are there.
I have come to the conclusion that there are 2 Flitter/Fritter families in Thatcham at the same time. From familysearch there is a James Fritter with spouse Matha. Can't find a birth for this James. I have found 4 sons so far with the same names as your Flitter family. Joseph and Benjamin, chr. 30 June 1765, John chr. 15 May 1769 and William chr. 21 May 1780. Can't find a marriage for James and Matha, probably around 1765 ish. I would think that the 2 families are related in some way back beyond 1750 or so.
Dave