UKIP's candidate for this week's Croydon North by-election has sparked controversy by likening adoption by gay couples to "child abuse".
Winston McKenzie described families headed by same-sex parents as "a hideous idea" and "unhealthy", claiming that children grow up unhappy in such families.
He said: "This business of gay adoption is tantamount to child abuse. It is unhealthy. The child has no chance to turn out normal.
"Many children grow up to be very unhappy."
Mr McKenzie claimed that youngsters would turn to homosexuality if offered no alternative.
"People are turning to this hideous idea because there is nothing else," he said. "We are a predominant Christian country and we need to return to that. These issues did not exist in the Bible."
He dismissed the suggestion that his stance could lose him votes in Thursday's byelection.
Mr McKenzie's outburst comes days after Rotherham Council removed three children from a foster couple because they were UKIP members.
UKIP has distanced itself from Mr McKenzie's comments, with London chairman David Coburn saying the party wholeheartedly supported equal rights for couples regardless of their sexuality.
Gay Rights charity Stonewall strongly criticised Mr McKenzie's beliefs, stating 19th century views were not acceptable in the 21st century.