Cabinet ministers Mark Spencer and Jacob Rees-Mogg were among 19 Tory MPs who discarded facemasks in the House of Commons for the final Prime Minister’s Questions before the summer break.

As Boris Johnson, self-isolating at Chequers, debated Sir Keir Starmer virtually, a clear political dividing line opened up over wearing face masks between the Conservative and Opposition benches.

While one in two Tory MPs was wearing a face mask, every Labour and SNP MP wore one. Only two DUP MPs on the Opposition benches were not wearing masks.

Government guidance is that people should wear masks in enclosed places where they might come into contact with someone they do not know.

However, The Telegraph counted 19 Conservative MPs wearing masks and 19 who were not wearing one.

Other Conservative MPs who refused to wear a mask included Andrew Murrison, Rehman Chishti, James Gray, Lee Anderson, Robin Millar, Sir Desmond Swayne, Alec Shelbrooke, Dehenna Davison and Andrea Leadsom.

The MPs were defying a plea from Sir Lindsay Hoyle, the Commons speaker, who on Monday made a statement to "strongly advise" the wearing of masks "in areas they consider crowded, including the chamber".

Facing the Tories, all 54 Labour MPs woremasks. Sir Keir had asked his MPs to wear them and put his back on after his six questions to Mr Johnson.

A Commons spokesman said: "The Speaker has no power to prevent democratically elected members from coming on to the estate or the chamber when the House is sitting.

"As such, there is no meaningful way to enforce a requirement on members to wear a face covering. However, throughout the pandemic, the Speaker has taken very seriously the House of Commons Commission’s duty of care towards all members of the parliamentary community, and he continues to strongly encourage all to wear masks."