Two prisoners have been arrested over the death of an inmate at Pentonville jail that led to a visiting former Olympic athlete being caught up in a lockdown.Another two inmates remain in a critical condition in hospital after the stabbing attack at the north London prison on Tuesday afternoon.Dalton Grant, who represented Team GB in the high jump at three Olympic Games, was giving a motivational talk at the prison when the incident took place.The 50-year-old told on Twitter how the prison was put into “lockdown” following the attack and he had to stay for several hours longer than planned. According to a HM Inspectorate of Prisons report in February last year, the prison sees a rapid turnover with more than 100 new prisoners a week and it was “performing poorly” as a result of staff shortages, overcrowding and prisoners’ easy access to drugs.Nick Hardwick, then chief inspector of prisons, also noted in his report: “Most prisoners felt unsafe; levels of violence were much higher than in similar prisons and had almost doubled since the last inspection.”Former prisons minister Andrew Selous insisted money was being invested in recruiting new staff and building modern jails.”What has happened is horrendous. I have met the parents of prisoners who have been murdered and it is horrific and my deepest sympathy goes out to all those affected,” he told BBC Radio 4’s Today programme. Meanwhile, the Prison Governors Association (PGA) has renewed calls for a public inquiry into the state of jails in England and Wales following the death.The union said Government cuts to staff and resources meant the “tragedy” at Pentonville was “no massive surprise”.The most recent statistics published by the Ministry of Justice showed there were 100 apparently self-inflicted deaths in the year to March – the highest for more than a decade.There were more than 20,000 assaults – 2,813 deemed “serious” – in the 12 months to December, a rise of 27 per cent year-on-year, and nearly 5,000 attacks on staff – a jump of more than a third compared with 2014.John Attard, PGA national policy officer, said: “It is no secret that we have had concerns about cuts and resources over the last four years. The Ministry of Justice (MoJ) statistics paint a very grim picture indeed.”Sadly, it comes as no massive surprise to anybody close to this that we have had a tragedy such as this.”The Prison Service paid staff to leave, the years of experience, the mentoring, the sharing of their experiences – a lot of that has been lost, and it is showing. It’s why we need an inquiry into this.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Officers and paramedics from London Ambulance Service were called to Pentonville at around 3.30pm on Tuesday where they found three prisoners with stab wounds.One, a man in his 20s, was pronounced dead at the scene at 4.25pm.The two other men, aged 21 and 30, were taken to an east London hospital where they remain in a critical condition, a Metropolitan Police spokesman said.Two men, aged 34 and 26, remain in custody. The Prison Service confirmed it is investigating.HMP Pentonville is a category B Victorian prison which opened in 1842 and holds more than 1,200 adults. The victim was an inmate at Pentonville Credit:Anthony Devlin /PA Violence broke out at Pentonville prison on Tuesday afternoonCredit:Jonathan Brady/PA We now ask for the Ministry of Justice to fully investigate this matter and the underlying problems within the prison estatePrison Officers Association Giving a talk at Pentonville prison today. Great to give back had to stay for a few hours longer. Someone got hurt. Lockdown.— Dalton Grant (@Dalton237) October 18, 2016 “The Government absolutely gets the seriousness of the violence issues, there is a huge amount of work being done to reduce violence.”But he said: “We absolutely need more officers on the wings,” adding that ministers had promised extra funding.The Prison Officers Association (POA) said it “once again” has serious concerns following the incident.In a statement, the union said: “The actions of the staff at Pentonville maintained good order and discipline and prevented this situation escalating.”The POA said it will not make further comment “other than to say the unprecedented rise in violence in all of our prisons must not be underestimated”.It added: “We now ask for the Ministry of Justice to fully investigate this matter and the underlying problems within the prison estate.”A Ministry of Justice spokesman said: “The Secretary of State has been clear that safety in prisons is fundamental to the proper functioning of our justice system and a vital part of our reform plans.”We are fully committed to addressing the significant increase in violence, self-harm and self-inflicted deaths in our prisons.”Earlier this month the Justice Secretary announced an immediate investment of an additional £14million in ten of our most challenging prisons, increasing staffing levels by over 400 prison officers.”In the coming weeks she will be publishing a White Paper setting out plans across the estate for prison safety and reform to 2020 and beyond.”Plans to shut old Victorian jails have also been outlined as part of a modernisation drive, with only HMP Holloway in north London confirmed as facing closure so far.