The UK government coalition's austerity drive will get under way in earnest today when the Chancellor unveils some of the biggest spending cuts ever attempted in the Western world.

George Osborne is expected to warn of a "hard road" ahead as he details £83 billion of reductions to tackle the deficit, which will see nearly 500,000 public sector jobs culled over the next four years.

Departments are facing budget cuts averaging 25% as part of the long-awaited Comprehensive Spending Review (CSR), with the Ministry of Justice (MoJ) and Department of Work and Pensions set to be among the hardest hit.

Unions reacted with fury after it emerged that more than 14,000 jobs could go at the MoJ alone, most of them front-line prison and probation workers. Legal aid and the courts are also expected to be targeted.

At the DWP, there is speculation that 'universal' handouts such as child benefit and winter fuel payments could be limited to save money, on top of a major crackdown on sickness and housing benefit.

The Secretary of State, Iain Duncan Smith, is believed to have promised big savings to get the Treasury to agree to fundamental reform of the welfare system in the longer term.

Ministers have also forced the BBC to take over funding the World Service, which was previously bankrolled by the Foreign Office. Together with a six-year freeze in the licence fee at £145.50, it means an effective 16% cut in the corporation's budget.

Commuters are braced for sharp rises in train fares as the Department for Transport withdraws rail subsidies, and thousands of police officers could go as the Home Office trims costs. Meanwhile, the social housing budget is likely to be more than halved to save billions of pounds.

The least affected is thought to be the Department for Education, which has secured an overall 5% reduction.

Even the NHS and Department for International Development, which are protected from the curbs, have been ordered to make sizeable efficiency savings to ensure that cash is not wasted.