The country’s most senior prison inspector has demanded the Justice Secretary take action over the squalid and dangerous conditions at HMP Bristol.

Peter Clarke invoked a rarely-used protocol forcing David Gauke to respond publicly after inspectors found high levels of violence, filthy cells and poor training and education.

Mr Clarke warned the Justice Secretary that the category B men’s prison had not improved at all despite being placed in special measures after a worrying inspection in 2017.

In the letter, Mr Clarke said inspectors had found rates of self-harm had increased since 2017 and remained higher than most local prisons.

Despite two suicides since the last inspection, recommendations for improvements had not been implemented and inspectors saw instances of “very poor” care of at-risk prisoners.

Inspectors also found the prison to be dirty, with many of the 600-plus inmates living in overcrowded cells.

Recorded levels of violence, a lot of it serious, were found to have increased since the 2017 inspection, and was much higher than average for local prisons.

Nearly two thirds of prisoners said they had felt unsafe at some point while held in HMP Bristol, and over a third said the currently felt unsafe.

A hotline for family and friends of prisoners in crisis to report their concerns had not been checked for over two weeks before the inspections, Mr Clarke said.

It was found the prison had enough activity places for all prisoners to take part in education, training or work for at least part of the day, but only half of prisoners had been allocated an activity.

Of these, on average only half attended their activity.

Under the terms of the urgent notification protocol, within a month the justice secretary must come up with a plan to improve the prison.

In the letter, Mr Clarke said: “The chronic and seemingly intractable failings at Bristol have now been evident for the best part of a decade.”

He added the prison had “demonstrably been in a state of drift and decline for many years” and that additional investment had not led to any visible improvement in conditions.

Mr Clarke said: “Some of the efforts to improve have, in reality, been a case of too little, too late.

“Some we saw had only just been implemented, and some were introduced during the inspection itself.

“On the basis of this latest inspection, I can have no confidence that HMP Bristol will achieve coherent, meaningful or sustained improvement in the future.”

The urgent notification protocol was added to the existing protocol between the prisons’ inspectorate and the Ministry of Justice in November 2017, signed by then-justice secretary David Lidington.

Bristol is the fifth prison to trigger the protocol since it came into force, Mr Clarke has also demanded urgent action over HMPs Nottingham, Birmingham, Bedford and Exeter.

The unannounced inspection took place between May 20 and June 7 of this year.

Prisons Minister Robert Buckland said: “We know Bristol faces serious challenges and we have been providing additional support.

“That has resulted in more prison officers and reductions in drug use, but some of the chief inspector’s findings make very difficult reading and it is clear that much more work is needed.

“We have immediately addressed the issues around prisoner phone support lines to make sure those problems can never happen again, and will publish an action plan within 28 days to reduce violence and self-harm and help turn the prison around.”