I am having trouble finding the birth certificate of my g grandfather George Roberts. According to the 1891, 1901 census and his army records, he was born in Trowbridge, Wiltshire. He enlisted in the 1st battalion The Wilts' regiment at Trowbridge on 19th June 1860 at the age of 18. He spent 22years in the army, most of them in Canada & India. He was discharged on 18th April1882 aged 40 years & 4 months (born about January 1842). He was married in India to a 25year old widow and names his father as James Roberts deceased. I have contacted the Wiltshire Registrar and the GRO but there is no record of a George Roberts for around that date. I am thinking he was born illegitimate and his mother married a James Roberts who gave him his surname.
Can anyone advise me what to try next.