The Conservatives have removed a decade of speeches from their website and from the main internet library – including one in which David Cameron claimed that being able to search the web would democratise politics by making "more information available to more people".

The party has removed the archive from its public website, erasing records of speeches and press releases from 2000 until May 2010. The effect will be to remove any speeches and articles during the Tories' modernisation period, including its commitment to spend the same as a Labour government.

The Labour MP Sheila Gilmore accused the party of a cynical stunt, adding: "It will take more than David Cameron pressing delete to make people forget about his broken promises and failure to stand up for anyone beyond a privileged few."

In a remarkable step the party has also blocked access to the Internet Archive's Wayback Machine, a US-based library that captures webpages for future generations, using a software robot that directs search engines not to access the pages.

The Tory plan to conceal the shifting strands of policy by previous leaders may not work. The British Library points out it has been archiving the party's website since 2004. Under a change in the copyright law, the library also downloaded 4.8m domains earlier this year – in effect, anything on the web with a .co.uk address – and says although the Conservative pages use a .com suffix they will be added to the store "as it is firmly within scope of the material we have a duty to archive". But the British Library archive will only be accessible from terminals in its building, raising questions over the Tory commitment to transparency.

Computer Weekly, which broke the story, pointed out that among the speeches removed were several where senior party members promised, if elected, to use the internet to make politicians accountable.

"You have begun the process of democratising the world's information," Cameron told the Google Zeitgeist Europe conference in 2006. "By making more information available to more people, you are giving them more power." That speech has been removed from the Tory party website and the archive. But users can find it on the Guardian website.

"It's clear to me that political leaders will have to learn to let go," Cameron told Google a year later, in another removed speech. "Let go of the information that we have guarded so jealously."

"We need to harness the internet to help us become more accountable, more transparent and more accessible – and so bridge the gap between government and governed," said George Osborne in 2007, in a third removed speech.

Computer Weekly's Mark Ballard, who broke the story, told the Guardian that it "shows how fragile the historic record is on the internet".

A Conservative spokesman said the changes to the website would improve the experience for visitors. "We're making sure our website keeps the Conservative party at the forefront of political campaigning," he said. "These changes allow people to quickly and easily access the most important information we provide – how we are clearing up Labour's economic mess, taking the difficult decisions and standing up for hardworking people."

The Wayback Archive was used by the Guardian last year when it began to investigate the software company set up by the Tory party chair Grant Shapps, who used the name Michael Green in the business. Traces of his family firm, which marketed software that the police said if sold could constitute the offence of fraud, disappeared from the archive a few weeks after the newspaper printed stories about Shapps. A slew of websites disappeared, leaving no trace of Michael Green's offer to make $20,000 (£12,500) in 20 days "or your money back" or details of phone lines offering expert internet marketing advice for $297 an hour.

Using a file named "robots.txt", website owners can tell computers that automatically scan the internet (called "crawlers") which parts of their sites to access. At the same time as the speeches were removed from the Tory party site, the Conservatives' robots.txt file was updated to prevent crawlers visiting the pages the speeches had been stored on.

The Internet Archive, which maintains the world's largest archive of old and defunct webpages, deletes its records of any site blocked by robots.txt.

Google's copy of some of the removed pages is still available, allowing readers to verify that where the website once displayed, for example, Cameron's speech on the "big society" in March 2010, it now just shows a 404 "page not found" error.