Assaults and drug use have dropped across 10 English prisons involved in a pilot scheme launched last year to tackle violence in troubled jails.

Positive drug tests fell by roughly half between August, when the £10 million scheme was launched, and March this year, according to figures released by the Ministry of Justice.

The rate of assaults dropped by almost 16% from the three months up to August last year to the latest quarter up to June, the data shows.

However, analysis by the charity Inquest suggests deaths increased across the prisons involved in the project, while Labour criticised the pilot, pointing out that only seven of the 10 jails saw a fall in assaults.

Measures including new scanners, sniffer dogs and repairs to basic infrastructure were introduced under the pilot at Hull, Humber, Leeds, Lindholme, Moorland, Wealstun, Nottingham, Ranby, Isis and Wormwood Scrubs prisons.

Ministry of Justice (MoJ) officials said “tangible results” were expected within 12 months, and then prisons minister Rory Stewart vowed to resign if the campaign failed. He was promoted to international development secretary before moving to the back benches.

Last week, Boris Johnson announced £100 million of investment to boost security and cut crime in prisons and on Thursday prisons minister Lucy Frazer said she was “encouraged” by the results of the pilot.

“We are already using what has worked to improve the rest of the estate, spending £100 million on airport-style security to stop the scourge of mobile phones and drugs that fuel crime and disorder in jails,” she said.

“Alongside our recruitment of thousands of prison officers and building 10,000 additional prison places, we will continue our relentless drive to protect the public and make prisons places of safety and rehabilitation.”

The MoJ said the project will end but will form “part of our continuing efforts to boost safety, security and decency in all prisons”.

The figures suggest the rate of positive drug tests across the 10 prisons roughly halved from 26.5% in August last year to 13.4% in March, although the MoJ report pointed out the number of prisoners sampled was relatively small.

The rate of recorded assaults per 1,000 prisoners across the 10 jails fell from 42.9 in the three months to August last year to 36.1 in the quarter to June – a decrease of around 16%, compared with a drop of roughly 8% across all prisons in England and Wales.

Two of the prisons involved in the pilot – Nottingham and Wormwood Scrubs – saw more assaults, while the rate at Hull remained roughly the same.

Charlotte Pickles, director of the Reform think tank, described the results as “very encouraging”, but said the findings must now inform how the promised £100 million investment should be spent.

“Violence is a critical issue across the prison estate. The 10 prisons are a small proportion of the estate, and do not include some of the worst in the country, which must now be the focus of attention,” she said.

“It is also vital that the Government does not undermine this progress through its ill-conceived sentencing proposals.

“Locking more people up for longer will create more demand in an already overstretched system, further exacerbating violence. Prison must always be a last resort.”

Figures released last month by the MoJ showed assaults in prisons across England and Wales hit a new high of 34,425 in the 12 months to March, up 11% from the previous year, and a rate of 415 incidents per 1,000 prisoners.

Data compiled by Inquest found there were 34 deaths across the 10 prisons involved in the pilot in the 12 months before the project was launched, while the charity’s analysis of MoJ figures found 41 deaths in the 11 months since the start of the scheme.

Deborah Coles, director of Inquest, said: “The 10 prisons project was fundamentally flawed in its scope and analysis of the prison crisis.

“It was a complacent, simplistic response to a complex problem. It was not about safety, but about security and control.”

“The relentless focus on the issues of violence and drugs may have brought some short-term relief in eight (of 188) prisons.

“However, it has abjectly failed to guarantee the health and safety of prisoners or reduce deaths according to the MoJ’s own data.”

Shadow justice secretary Richard Burgon said: “Focusing on a small number of cherry-picked prisons was a blatant attempt to distract from the wider Tory-created chaos across our prisons system.

“That violence has continued to increase even in some of these targeted prisons highlights, once again, the Tory failures at the heart of our prisons system.

“The wider reality is that, in the year since this project was launched, prison violence has reached record new highs and more prisons are now labelled as being of serious concern than ever before.”