The National Archives have provoked outcry from academics by announcing a new trial restricting readers to 12 documents a day, despite concerns it may add “huge expense” to research.

Visitors have traditionally been able to browse as many documents as required from the vast repository in Kew, west London, which holds records spanning more than 1,000 years of British history. 

But, from the end of March, a six-month trial will begin that imposes a cap of 12 documents per day on each reader, allowing an additional 12 if requested in advance. 

The National Archives claimed the move was designed to increase efficiency - but faced an immediate backlash from historians who complained their work could become untenable. 

Guy Walters, the author and Second World War historian, said he was “really concerned” about the measures, claiming they could “badly affect how much work historians can get done”.

Mr Walters warned the changes would heap “huge expense” on researchers by requiring them to set aside more days in Kew to find the documents they needed.