Two departments, the Department for Transport and the Department for Communities and Local Government, have migrated onto the GOV.UK site, the Cabinet Office said on Thursday.
In addition, three associated agencies and bodies – the Driving Standards Agency, the Building Regulations Advisory Committee (BRAC) and the Planning Inspectorate – have also moved to the new domain.
The Cabinet Office said hundreds more government websites will also move to the new platform over the next 18 months. Over time, in addition to savings made from closing the DirectGov and Business Link sites, the move is expected to save the taxpayer at least £50 million annually, it said.
Once the move is completed, the Cabinet Office says users "will be able to track government activities in a clear, consistent and transparent format".
Government policy, announcements, publications, speeches and other corporate information will be presented on the new platform, with the ability to search by topic and organisation.
"The driving principle behind GOV.UK is that it should meet the needs of users and what they want to do, and not how government wants them to do it," said Cabinet Office minister Francis Maude. "It is a simpler, clearer and faster way for people to find government services and information online."
Cabinet secretary Sir Jeremy Heywood said GOV.UK will allow people to find definitive information about what the government is doing in one place.
"Presenting policy information in this way will help the civil service to become more open in the way it works as set out in the Civil Service Reform Plan," he said. "It will become much easier for civil servants to understand the wider context when they are developing and implementing policy and for the public to access the information they need."
In 2010, UK digital champion Martha Lane Fox called for radical improvement to government internet services.
This included shifting 30% of government service delivery contracts to digital channels to save £1.3 billion annually, in addition to simplifying digital public services into a single domain.