I can find no trace of him in pre 1881 censuses. I'm afraid it's hard cash time, as I think you need both the marriage cert and the 1845 birth cert to confirm that it is the same father on each of them.
Do you have the birth certificates of any of the children evidencing that Robert was the father? It's slightly odd that in 1891 when Robert was alive they were all enumerated as Gentle, yet once he was dead, in 1901 (Clarke) and 1911 they were enumerated as Clark. What name did the children use when they married? If Robert was the father of Harry who you say was born in 1881 then he should have been in Stotfold or thereabouts on 3 Apr 1881. So where was he??
Thank you for that David.
The only birth certificate I have is for Harry Gentle which has Robert down as the father, and Ellen as mother. I wonder if Robert was a plasterer. Could he have been moving around the area?
I am going to send for Robert and Ellens marriage certificate, and think it is worth a punt on the 1845 birth cert.
Most of my family lines I can trace back to the distant past, with this exception. I am totally confused. As you say, in 1881 they are using Gentle and in 1901 Clarke. The only thing I can say with certainty is that my GG Grandfather Harry used the name Gentle throughout his life, and family members can remember Nellie, who also used the name Gentle.
It may be a case of order and wait.
Steve