British politics risks an unprecedented shift to the far right as a result of public disillusionment if a Labour government fails to enact radical change, the former shadow chancellor John McDonnell has warned.

Writing in the Guardian, McDonnell said the threat would come not just from Nigel Farage’s resurgent Reform UK but from the return of a Conservative party “shorn” of its moderate wing and dominated by populists.

McDonnell, who served in the shadow cabinet under Jeremy Corbyn, reflected the views of others on his party’s left who are impatient with what they regard as Labour’s too-cautious approach. “The central messaging of Keir Starmer’s electoral strategy is that he’s not Jeremy Corbyn and that Labour is not the disaster that is the Conservative party,” he said.

McDonnell pointed to the polling figures of Reform UK, reaching as high as 11%, as evidence of “how a far-right populist programme can pull the major parties on to a rightwing agenda”.