Sir Keir Starmer has reopened the debate on welfare reform, saying there is a “moral case” to cut rising benefit claims for mental health problems.

The prime minister said Labour would have to “look again” at how to deal with increasingly costly claims for anxiety and depression, arguing that the money would be better spent on treatment.

Senior ministers are beginning to talk about another attempt on welfare reform after a chaotic U-turn in the summer, when previous effort to make £5 billion of cuts was rejected by Labour MPs. Rachel Reeves, the chancellor, also told the Labour Party conference that “we can’t go on like this” as she stressed cost had to be controlled.

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Starmer’s failure to force through cuts means that spending on sickness benefits is on course to hit £100 billion by the end of the parliament, twice what it was in 2018. Claims are growing fastest for mental health problems: 250 people a day were given personal independence payments (Pip) for anxiety and depression during Labour’s first year in power.