Economist Jonathan Portes assesses how well the government has implemented its controversial welfare reforms. The government describes the programme as "the most ambitious, fundamental and radical changes to the welfare system since it began".

When the Coalition came to power in 2010, welfare - not including pensions - was costing the country nearly £100 billion a year. Iain Duncan Smith, the secretary of state for work and pensions, was given the task of making work pay and - in so doing - taking millions of people off benefit and saving the country billions.

Influential figures from parliament, the civil service and one of Iain Duncan Smith's closest advisers offer revealing accounts of what's been happening during those past 4 years.

Economist Jonathan Portes asks whether these changes are a vital strategy to stem a welfare system spiralling out of control or - as some argue - nothing short of a fiasco, which has caused genuine hardship?

Producer: Adele Armstrong.