Just a side note re the surname.
Percival Sands WILKINSON was born in Islington in 1892. He appears by that surname in censuses.
His brother was Challinor Sands Wilkinson, who married twice as Chaloner W Sands and died in 1954. There were births to both marriages, in case you wanted to follow up Percival's brother's family. There is a reference to Chaloner's 1929 bankruptcy in Hertfordshire here:
http://www.edinburgh-gazette.co.uk/issues/14592/pages/1230/page.pdfand to his son as executor of perhaps his maternal aunt here:
http://www.london-gazette.co.uk/issues/52852/pages/3943/page.pdfHis mother was Edith Emma Sands who married Frederick James Wilkinson in 1890 and was widowed by 1901, and she and her children lived with her parents. I wonder whether she was really widowed, or estranged and Percival took her surname. Frederick J Wilkinson was a post office clerk in 1891, born in Stoke on Trent c 1861.
Hm, I had discarded the FJ Wilkinson who died in Luton in 1899 aged 40, since he matched a birth there in 1858, and that doesn't match the info in the 1891 census. But according to trees at Ancestry that is the one, husband of Edith Emma Sands and son of Allen Wilkinson and Eliza Challinor ... a marriage that actually happened in Stoke on Trent, sigh. (The Luton one married someone else altogether.)
No birth of a Robin Wilkinson to fit either though.

Much of this may well be known, I've just been poking at it to try to find some clue about Robin and nothing has emerged.