Iain Duncan Smith is to remain in charge of welfare reform across the UK after prime minister David Cameron decided to retain him as work and pensions secretary in his new Conservative government.

Downing Street said Duncan Smith would continue with his task of “making work pay and reforming welfare” as the government implements the Universal Credit reforms and imposes £12 billion in cuts on the welfare budget.

Mr Duncan Smith’s first five years in the job were marked by deep issues with the roll-out of the flagship Universal Credit system and anger over cuts to disability payments. The cuts are likely to be one of the most contentious areas of the new government amid suggestions that they could involve limits to child benefit, housing benefit and child tax credits.

Mr Duncan Smith said: “It is a privilege to serve in the government, and I am delighted to have the opportunity to complete the vital welfare reforms that have already helped so many people back into work. The completion of Universal Credit will ensure work always pays, and will improve the incomes of those on low salaries.”

George Osborne is considering whether to hold an emergency budget within the next month to set the framework for an autumn spending review in which he will outline the details of the cuts as part of a planned £30bn fiscal consolidation.

The chancellor, who has been given the additional title of first secretary of state by the prime minister, plans to eliminate the budget deficit by 2018-19 by imposing £12bn in welfare cuts, reducing day-to-day government spending by £13bn and raising £5bn from tax-avoidance measures.