Ads will feature on 800 bus-sides, following the success of the organisation's previous high-profile fundraising appeal.
To date, the BHA's first bus drive has raised more than £126,000 - 23 times its target. The next wave of ads will appear on buses in all major UK cities, including 200 in London, where it will also run Tube ads.
The appeal launched in October with a mocked-up picture of a bus carrying an ad proclaiming: ‘There's probably no God. Now stop worrying and enjoy your life'.
The drive's initial aim was to raise £5,500 by the end of the year, which would pay for 30 bus-side ads in central London. However, it raised more than £50,000 in its first day, assisted by large amounts of publicity and public support from Dawkins.
Fresh bus ads will carry the original slogan, but the tube ads, which are being kept under wraps, will be different.