Cotton MS. Augustus II. 106, one of four surviving exemplifications of the 1215 text.

Darren Jones, the chief secretary to the prime minister, told Sky News that the 1215 charter enshrined a right to “timely” justice.

He argued that the current record backlog of almost 80,000 Crown Court cases means victims and defendants are now routinely denied that right.

Jones pointed to clause 40, which promises: “We will not sell, or deny, or delay right or justice to anyone.”

A Conservative source said Labour was “desperate” in relying on a selective reading of Magna Carta to justify reducing access to jury trials.

Leaked Ministry of Justice documents show that David Lammy, the justice secretary, is considering limiting juries to cases involving murder, rape, manslaughter and other offences attracting sentences of more than five years.

Under the plan, trials for offences with a sentencing ceiling of up to five years would be heard by a judge sitting alone. Magistrates’ sentencing powers would also be extended from 12 months to two years, further reducing the range of cases eligible for a Crown Court jury.

Offences such as burglary, affray, fraud, certain sexual offences and criminal damage under £10,000 would no longer carry an automatic right to elect jury trial. Complex fraud, financial crime and cyber crime cases would also be allocated to judge-only hearings.

The leaked proposals include removing the automatic right of appeal, replacing it with a requirement to seek permission.

Officials argue the reforms are necessary to prevent delays stretching into the late 2020s. Critics say they would dismantle a core constitutional safeguard that has existed for more than eight centuries.