Theresa May has been blamed by chief constables for botched police reforms that led to tens of thousands of alerts on foreign criminals being kept from their home countries.

She is accused of “starving” the crucial police national computer (PNC) of money against advice from forces when she was home secretary, and instead pushing ahead with an ambitious and costly super-database to replace it that is now years behind schedule and millions of pounds over budget.

Her decision is said to have led to serious problems developing with the “creaking” PNC – including its failure to send details of 75,000 foreign nationals convicted in the UK to their home countries, in a scandal revealed by the Guardian this week.

The Home Office is now desperately trying to fix the software glitch that has gone unnoticed for five years, while May’s planned replacement system – known as the Law Enforcement Data Service (Leds) – is now due to cost £469m and will not be working fully until 2023.

The former Durham chief constable Mike Barton told the Guardian: “It doesn’t surprise me that there are problems with the PNC, it’s a creaking database, but the Home Office chose to delay its replacement with a new system, Leds.

“PNC is old and the Home Office is starving it of money to keep it going, they have siphoned off hundreds of millions of pounds from it and other vital police systems for the Leds programme, which is overspent, late and will not do what police systems require. I think it’s a disgrace how much money they are wasting on Leds.

“The public are not safe because of decisions made in the Home Office.”

Former Thames Valley police chief constable Peter Neyroud, now a director at the Institute of Criminology, University of Cambridge, said: “Home Office – both political and civil service – leadership of these issues has not served the public interest well.

“These systems are fundamental to the safety and security of every one of us. The failure to manage them properly over the last decade is a national scandal, which could properly be added to the long list of problems that the recently announced Royal Commission on Criminal Justice has to deal with.”

The latest update on big Home Office projects, published in July 2019, admitted that the Leds super-database had been given a “red” rating in a review – meaning it could be undeliverable. It was first announced by May in 2016 as part of her modern crime prevention strategy.

The report revealed that costs for Leds in 2018-19 alone had risen by 22% to reach £82m, putting the overall price tag of the scheme at £469m.

A Home Office budget estimate submitted to parliament in May 2019 insisted the super-database would “create a cheaper, more flexible IT infrastructure that will provide better information and link more data between law enforcement and public protection agencies”.

But it admitted the programme had been “recently reset” and the new target was for the old PNC (which holds details of millions of convictions) and PND (covering intelligence reports) to be switched off in 2022 and 2023 respectively.

As the Guardian revealed, a software error with the PNC dating back five years has meant that an estimated one in three conviction alerts on foreign nationals has not been sent to police in their home countries.

And minutes of a board meeting by the international criminal records office show that the backlog of missed notifications may never be passed on to EU countries – because the Home Office fears the “reputational impact”.

MPs are calling for an inquiry into the scandal. Stephen Doughty, a Labour member of the home affairs select committee in the last parliament, said: “It is vital the new home affairs committee takes this up urgently once constituted, and I and other members will be asking questions urgently of ministers.”

He went on: “It is clearly in our mutual interest to exchange as much information as possible on, for example, serious criminals, paedophiles and terrorists with trusted partners – and the revelation of yet another screw-up from the Home Office could put this crucial relationship at risk.”

The software error has still not been repaired and so more and more alerts are being missed every day, sources confirmed last night.

However, no cases have yet come to light where dangerous offenders have slipped back to Europe undetected to commit further offences as a result of the missing data.

The revelations were raised in parliament on Wednesday, with the Labour peer Lord Kennedy of Southwark telling the House of Lords that the Guardian’s “revelation is both shocking and worrying”.

He asked: “Does the minister accept that this is a huge failure on the part of the government and that it is possible that dangerous offenders have returned to their home country without the UK making proper notification to the authorities?

“When the error was discovered, it was not corrected – shamefully – because of the risk of reputational damage to the UK.”

Responding for the government, Lord Bethell admitted: “The noble lord is entirely correct: this is a very serious matter and the government take it very seriously.”

He blamed the out-of-date police computer systems and insisted: “We are currently working hard to upgrade our legacy systems. The central authority for the exchange of criminal records is working at pace to implement the technical fixes which will ensure that all the correct data is shared with EU members.”

The Home Office said: “The Police National Computer and Police National Database will be replaced by the new Law Enforcement Data Service.

“Given the complexity, it will now be delivered through a phased approach starting this year and is on track for completion in 2023. The new system will save £216m when rolled out nationally. We will continue to monitor progress to ensure the successful delivery of this programme.”