The arbitrary 1% cap also ignores rising inflation and the increasing disparity in pay between the public and private sectors, said the union for 27,000 professionals, managers and specialists across the civil service and wider public sector.

“The Treasury’s cut-and-paste approach to pay ignores a fundamentally changing world,” said Prospect deputy general secretary Garry Graham.

“The civil service needs to recruit, retain and motivate highly skilled people capable of delivering Brexit, major infrastructure projects and other policy initiatives.

“But since 2013 pay rates in the private sector have been significantly outpacing those in the public sector. The living standards of our civil service members have fallen by 15%-20% in the past seven years and the service is at its smallest since 1939.

“This gulf will get wider unless the government acts immediately. Alarm bells should be ringing,” said Graham.

Prospect called on the government to take a more sophisticated, evidence-based approach to the pay of specialist staff.

“We need an independent pay review body for the civil service. Its first task must be to assess the growing gaps in the rates paid for comparable jobs in the private sector,” said Graham.

“MPs’ pay is set by an independent body. If it’s good enough for them, it’s good enough for those who serve them.”