Audrey, I can find Frank aged 14 in Maidenhead on the 1901 census index online, together with siblings Ethel (11), Arthur (8), Sidney (6) and Albert (4).I cannot see parents in the index, which may mean that they are mistranscribed or possibly father died mother remarried.The only way to tell would be to view the census image, which is pay to view, credit cards accepted.
I can also find an 8 year old Millicent Baker, the only Millicent in Maidenhead of about the right age, again I have siblings and 1 parent but cannot get the rest without paying.Interestingly they all come from Devon, not Berkshire at all!
I have a good grip on the Britnells generally and have the 1881 census on CdRom, it is now online as well, but there are no Britnells in Maidenhead in it.If your Britnells come from the Cookham (Berks) Branch of the family or the Oxfordshire or Buckinghamshire branches I can get you back with certainty to pre 1600 in Bucks, and with a good hint that the family can be traced back to a written record in 1366, I have yet to prove that last part but it is fairly convincing on circumstantial evidence.
To get back we need Franks parents, if you know those I can find them in 1881 and probably earlier as I have a lot of census information for earlier years as well which I have transcribed from the microfilm at the Family Record Centre in London.I am in Canterbury, Kent, England.
E-mail me off list at email@example.com and I'll see what I can do to help.