Seb Corbyn, the son of the Labour leader, has been dragged into a bitter power struggle between the shadow chancellor, John McDonnell, and his father’s office, which erupted last week in acrimony over Labour’s response to the budget.

Sources say Jeremy Corbyn is hurt that his son’s role for McDonnell has been downgraded from chief of staff after an influx of hard-left advisers into the shadow chancellor’s team.

McDonnell sparked anger among Corbyn’s team last week by stating publicly that Labour would not oppose the government’s plans to raise income tax thresholds in the budget.

That line was contradicted by Corbyn’s spokesman and by tweets emanating from the Labour press office. Shadow cabinet members openly questioned why Labour was supporting a tax cut for those