The Cameron government had previously announced plans to sharply curtail one of the government’s costliest benefits, an $18 billion program that has paid $32.50 a week to every family for a first child, and $21.50 for every subsequent child, until they turn 19. Starting in 2013, any parent earning more than $70,500 a year will lose the benefit payments. Another measure already announced will curb the $32 billion annual cost of government housing subsidies, limiting payments to low-income families to a maximum of $640 a week.

In some cases that British newspapers have highlighted in upmarket London neighborhoods like Kensington, immigrant families have been receiving housing subsidies exceeding $160,000 a year.

The Cameron government has said that the benefits programs are so prolific that billions of dollars go unclaimed because Britons are unaware the programs exist. Examples include funeral payments to those on low incomes; winter fuel allowances of $40 a week for pensioners; a “bereavement allowance” of up to $155 a week, for a year, for the death of a spouse or a civil partner; and a tax-free lump sum of $3,200 for those losing a spouse or partner who was under state pension age.

For the governing coalition of Conservatives and Liberal Democrats, now ending their first six months in office after ousting the Labour Party, the welfare reforms are at the center of a harsh austerity program hailed by influential economic bodies like the International Monetary Fund as a pacesetter for cutting growing government deficits across the industrialized world.

By focusing on welfare expenditures that account for nearly a third of Britain’s annual budget, the Cameron government aims to save about $30 billion, about 10 percent of its welfare outlays, over the next four years. But the wider cuts in government spending, amounting to $130 billion and averaging nearly 20 percent for most government departments up to 2015, are a huge political gamble. The risks became starker when 50,000 people, mostly students, marched through the Whitehall government district on Wednesday to protest education spending cuts and the stiff increase in college tuition.

The march set off scenes of violence that alarmed many Britons, fearful of a new era of street turbulence on a scale not seen since Prime Minister Margaret Thatcher’s economic overhaul in the early 1980s. Apprehension has spread as the full impact of the cuts begins to be felt. Labor unions have threatened coordinated strikes aimed at crippling government services. The welfare changes, affecting hundreds of thousands of recipients, could stir more unrest.