The site, which went live yesterday, aims to mobilise 2 million supporters to lobby on smoking in public, obesity, sunbed use and NHS cancer services. The scheme will run as a pilot until June.
The site's first campaign will ask existing supporters to encourage their MPs to support the introduction of smoke-free workplaces, without exemptions.
The Government's Choosing Health White Paper, published last November, outlined a partial ban on smoking in public places from 2008. But exemptions, such as allowing pubs that do not sell prepared food to choose whether customers can light up, meant it fell short of the full ban demanded by anti-smoking lobbyists.
Richard Davidson, director of policy and public affairs at CRUK, said: "We are asking our supporters to write to their MPs and parliamentary candidates to keep up the pressure so that the issue is on the political agendas of people who are running for Parliament at the forthcoming election."
He added that the charity's supporters will be asked to write to their MPs after the election to ensure that "improved" proposals are included in the next Queen's speech.
The campaign initiative also has an off-line element, which began last night. The charity organised a meeting at Whitehall, where campaigners from Ireland, Italy and Norway told MPs and peers of the effect of tighter smoking legislation on smoking rates, bar trade and compliance levels.
Davidson said the shift towards supporter-led campaigning was an obvious move, even for a charity renowned for its scientific research, because CRUK could count on the larger body of support gained through the 2002 merger. "We have a huge army of fundraising and volunteering supporters, who will be a very effective force if they can be mobilised," he added.
CRUK has created many public health awareness campaigns, although these have always been led from within. Davidson said the decision to engage supporters was made on the back of a wave of positive feedback it had received from supporters and MPs since last September.
The website will be managed initially by CRUK's five-strong parliamentary team, and has been granted a £10,000 budget. It will enable users to email their MPs and Scottish Parliament or Welsh Assembly members, sign petitions and vote in monthly opinion polls.
The charity's previous lobbying was restricted to loose alliances with like-minded organisations such as Action on Smoking and Health and the British Heart Foundation. These will continue alongside its new campaigns.
The site will be launched 'softly' through internal marketing and existing communications channels before targeting the public.