Mr Gallagher claimed that taking drugs was "like getting up and having a cup of tea in the morning".
He said most people in Britain took drugs and it was hypocritical of MPs to lecture pop stars on their comments about them as, he claimed, several people in Parliament were cocaine or heroin addicts.
He was speaking after the sacking of Harvey by his fellow band members after comments he made about drugs led to John Major, the prime minister, condemning the East 17 singer in the House of Commons and radio stations banning the group.
Gallagher, whose brother Liam was cautioned recently for possession of cocaine, said the whole affair had not been a "scandalous sensation" compared to Government arms sales.
He told BBC Radio: "If Brian Harvey did do 12 Es in one night - if he did do, and he's saying that he did - if he's being honest, then fair enough.
"If you can't be honest in this country then we might as well go and live in China, know what I mean?"
Gallagher added: "There's people in the Houses of Parliament, man, who are bigger heroin addicts and cocaine addicts than anyone in this room right now. And it's all about honesty at the end of the day.
"As soon as people realise that the majority of people in this country take drugs, then the better off we'll all be. It's not like a scandalous sensation, or anything like that. Not when you've got our Government selling arms to people who go out and kill probably relatives of somebody in this room.
"Drugs is like getting up and having a cup of tea in the morning."