I found out from reading a book called "The Secret Orchard of Roger Ackerley" by Diana Petre that until the age of majority was reduce from 21 to 18, illegitimate children legally reached their majority at 18.
This means they were able to vote, incur debts and, probably most importantly, not be prevented from marriage or running away.
The book itself is a fascinating account of a second family maintained by a man from 1910 through to his death in 1929.
What was even more interesting to me was that many of the characters in the book are known to me, through the fruit business of Elders & Fyffe , and then through the friends of the mistress( Muriel)/second family and her record in both World Wars.
I can't help but think many men would happily maintain such a double life. My own family, for instance, is convinced I have a second family in Luton Airport. That's the airport, not the town.
I don't think that's quite what would be wanted.