Cairns had been a member of a Catholic gang and was found in the research to have been in and out of prison at the time of the birth of Lulu's mother.
Kennedy was found to be the daughter of a Worthy Mistress of the Ladies' Orange Lodge 52 and explained why the two families were against the union between Kennedy and Cairns.
In the UK, "To Sir With Love" was released on the B-side of "Let's Pretend", a #11 hit.
In the late-1960s, Lulu's pop career in the UK thrived and she had several television series of her own.
After the success of "Shout", Lulu's next three singles failed to make an impact on the charts.
Her grandfather Hugh Cairns was a Catholic and her grandmother, Helen Kennedy was a Protestant.
Her next record, "Try to Understand" made the Top 30.