It may sound like a road safety campaign from the 70s, but today the Green Cross Code is just one example of how charities are harnessing the power of the internet to lobby political parties in the run up to the general election.

The Green Cross Code is an internet campaign run by Friends of the Earth (FoE). The idea behind it is not new. "Every pressure group asks supporters to write to their MPs," says Martin Williams, FoE spokesman.

However, there are problems with this traditional call to arms."The trouble is that many people don't know who their MP is, or what constituency they live in. Our website gives people access to this information by simply tapping in their postcode."

During the general election campaign supporters are able to find out who is standing in their constituencies. They are also able to download a template letter expressing their concern about environmental issues. This can be posted or faxed to the candidates. Alternatively, if they click a few more drop boxes on screen, the letter can be dispatched directly to the would-be MPs via email.

Williams stresses that FoE has been offering this type of service to supporters for years. The new technology has just made the process much more efficient. "We used to mail out huge lists of different candidates and addresses to supporters. The internet is very good for enabling people to sort out data quickly and easily."

While FoE has developed their internet campaign themselves, other charities are using the services of Advocacy Online. This internet service company develops and runs online campaigns for voluntary organisations.

During this election it is running a site for Age Concern which allows browsers and supporters of this charity to lobby candidates about issues affecting older people. Like the FoE site it generates details about parliamentary candidates based on people's postcode. It also allows browsers to send letters to the local media as well.

"Our target base is the 'silver surfer', the older people using the internet," says Age Concern's Emma Aldridge. "This site allows grassroots people to have their say. We provide model letters but we emphasise that they need to be customised and related to personal experiences."

Most voluntary organisations can also improve their campaigns by using the internet. Richard Hebditch, parliamentary officer at National Council for Voluntary Organisations says: "It offers the means by which supporters can lobby. It also provides the information for people to lobby themselves. All in all, it's very empowering."

Globe View 2001 is an alliance of 29 organisations, including Oxfam, Action Aid and Save the Children, seeking all-party action on international issues. Supporters can download Vote For Me campaign posters, which display pictures of children from the developing world.

The major environment campaigns have also come together to sponsor a site called vote-environment.org.uk. This allows the public to compare the main political parties' stance on key green issues. Again, it can generate personalised letters and emails but these can only be sent to party headquarters rather than the candidates themselves.

All campaigners are keen to know how many people take part and how effective they are. Technology provided by Advocacy Online allows Age Concern to do this. Graham Covington, its managing director, said: "When supporters send an email to politicians or the media from the site this triggers a follow-up email from Age Concern. This is sent to the supporter a fortnight later asking if they got a response."

Mr Covington argues strongly that online campaigning is not about "sending 10,000 emails to crash politicians' computers", rather, "it seeks to develop on line communities which, over time, will work and campaign together".

He says that online campaigning has not replaced traditional "off-line" techniques. In time, he argues, campaign groups will migrate to online campaigning because it is much easier to use.

Most campaign groups are keen to develop new ways to use the internet to improve their campaigning and to involve their supporter bases and advocacy work.

The Future Foundation's Joe Saxton shares this enthusiasm. He does, however, cast doubt over whether it will have much effect during the election period: "It's the one time when politicians are away from their PCs and laptops. They are in the real world talking to people on their doorsteps. Most will not have time to even open their emails."