Westminster politics is deliberately set up to keep power in the hands of major parties, Caroline Lucas, the only Green MP in Parliament, is expected to say.
In a speech at the Institute for Government on Wednesday evening, Lucas will argue that it is now almost impossible for small parties to stand candidates in enough constituencies to make a real impact on politics.
"If the Greens were to stand candidates in every seat in Britain it would mean spending over three hundred thousand pounds just in deposits," she will say. "That’s more than we’d have to spend on the entire campaign. And the question of how much you’d get back in saved deposits is not very relevant if you have no money left over for leaflets, posters or broadcasts."
Lucas will add: "The reality is that Parliament is this way for a reason: it keeps power in the hands of the whips and the leaders of the main parties," she will say. "They don’t want smaller parties or their own more independently-minded MPs to make full use of the powers of the institution, whether to legislate or scrutinise the government."
The MP will also argue that the continuing dearth of women in parliament - male MPs still outnumber women by 5 to 1 - "undermines the quality of law-making and scrutiny".
"A mix of ignorance of the problem and self-interest affect issues such as equal pay, rights for temporary and part-time workers, and funding for rape crisis and domestic violence centres," she will say.
There are some advantages to being the lone representative of your party in the Commons, however, Lucas will say. They include the freedom to submit your own amendments. It also strengthens parliament by ensuring that during a time of coalition there is still a fair level of opposition views represented.
"On so many issues, from setting up Academies to bringing in the private sector to run the NHS, the three main parties all line up on one side.
"So it falls to the Greens to make the alternative case. That is what we are doing, on climate change, fuel poverty, and a steady state economy, and on Afghanistan, electoral reform, public sector pensions, and many other vital issues."
The MP's speech will be live-tweeted from 6PM by @ifgevents using the hashtag #greenmp.