Ian Meller, who is standing for North West Leicestershire, was fined £400 in 2000 for carrying a plank of wood at the gay event.
He told the Leicester Mercury that he had picked up the plank to protect himself against members of the Anti-Nazi League.
Mr Meller said: "The wood was lying in the road – I was there because we were against gay relationships being promoted in schools.
"It was unfortunate, but it was momentary, I wasn't on my own and I regret what happened.
"To be honest, that incident opened my eyes and I left the National Front shortly after that because I could see street demonstrations couldn't get us anywhere."
Mr Meller said he joined the National Front because he was concerned about crime and immigration, although he did not regard it to be an extremist party.
He added: "In terms of gay people, the BNP's view is what you get up to in your own house, we don't want to know about it at all.
"What we are against is using public money to fund things like gay marches.
"I'm a Christian and my own view is marriage is between a man and a woman and it's for bringing up a family.
"I wouldn't outlaw homosexuality because we are all equal."
Last month, BNP leader Nick Griffin admitted that he finds gays "creepy" and would ban civil partnerships if his party won power.
He told Total Politics magazine that he would ban the promotion of homosexuality in schools but would consider gay adoption.
Mr Griffin said he would be "inclined to agree" with gay couples adopting, but only "if we reach the stage where there are so many children in children’s homes that you run out of would-be adopted ideal families".
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