Former prime minister John Howard has criticised suggested reforms to the political donations system, saying it is "fundamentally an attack on freedom of political activity and expression".

Mr Howard supported the idea of real-time disclosure of donations but said anything beyond that would stymie the ability of parties to run campaigns and lead to "massive increases in public funding".

"I don't believe that if a company is carrying on a lawful activity, it should be prohibited from making a political donation. I don't think every developer in this country is a crook any more than I believe that people who aren't developers are all virtuous. I don't agree with

that, and I certainly don't agree with the suggestions that we should further limit the amount that people contribute or companies contribute," Mr Howard told the National Press Club in Canberra on Wednesday.

"I think fundamentally it is an attack on freedom of political activity and expression. If you limit donations to a small amount per head, that will inevitably result in massive increases in public funding. And political parties cannot run campaigns on nothing."