A £140,000 atheist advertising campaign on buses was launched today with the slogan: "There's probably no God. Now stop worrying and enjoy your life."

A total of 800 buses across Scotland, England and Wales will carry the slogan from today and tomorrow following a fundraising drive which raised more than £140,000.

The buses will appear in Glasgow, Edinburgh and Dundee.

The fundraising drive was prompted by a suggestion from comedy writer Ariane Sherine, who received support from the British Humanist Association (BHA) and atheist campaigner Richard Dawkins.

Ms Sherine had objected to a set of Christian advertisements running on London buses in a piece written for the Guardian's The Comment is Free in June.

Speaking at the launch of the campaign in central London, Ms Sherine said the sheer number of donations received had demonstrated the strength of feeling in Britain.

She said: "This is a great day for freedom of speech in Britain and I'm really excited and thrilled that the adverts have been approved and I hope that they will make people smile on their way to work.

"I am very glad that we live in a country where people have the freedom to believe in whatever they want."

The buses that will carry the slogan outside London will run in Manchester, Birmingham, Glasgow, Edinburgh, York, Leeds, Newcastle, Dundee, Sheffield, Coventry, Devon, Liverpool, Wolverhampton, Swansea, Newport, Rhondda, Bristol, Southampton, and Aberdeen, the British Humanist Association said, in a four week campaign.

Ms Sherine, speaking at the launch, said she had objected to a set of Christian advertisements carrying a website address which when accessed warned that people who reject God are condemned to spend all eternity to "torment in Hell."

She said the total money raised reflected the strength of feeling from atheists and humanists in Britain.

"I think there have been a lot of people out there who have been looking at evangelical advertisements and not saying anything and thinking that these advertisements have been approved and just shrugging it off. Now finally they have an opportunity to express this feeling of exasperation."

She said the atheist campaign was a "rational and positive" reaction.

Professor Dawkins, who unveiled one of the London Underground advertisements said: "Across Britain we are used to being bombarded by religious interests, not just Christians but other religions as well who seem to think that they have got a God given right to propagandise and to take over things like Thought for the Day.

"In the House of Lords we have bishops sitting as of right, and we are still very much dominated by religious interests."

Other supporters at the launch including philosopher A C Grayling, Guardian columnist Polly Toynbee, and Graham Linehan co-writer of the Father Ted comedy series.