Ministers have been urged to renationalise probation services following an "extremely worrying" rise in the number of supervised offenders charged with serious crimes.
Justice minister Sam Gyimah said a total of 517 reviews were triggered in 2016/17 after an offender under statutory probation supervision was charged with murder, manslaughter, rape or certain other serious violent or sexual offences.
He added there were 507 such reviews in 2015/16 across England and Wales compared to 429 in 2013/14, 409 in 2012/13 and 441 in 2011/12.
Reforms introduced in 2014 saw the National Probation Service (NPS) created to deal with high-risk offenders while remaining work was assigned to 21 new Community Rehabilitation Companies (CRCs).
They replaced the former probation trusts and gave private firms a greater role.
Plaid Cymru Westminster leader Liz Saville Roberts raised concerns about privatisation in response to the 26.4% increase of serious further offence (SFO) reviews from 2012/13 to 2016/17.
Ms Saville Roberts, who unearthed the figures via a written parliamentary question, said: "This is an extremely worrying rise in serious crime committed by people who are supposedly under supervision.
"It is astonishing that ministers are claiming the difficulties faced since privatisation were unforeseen when a leaked internal risk management document shows that they were warned.
"These are offenders who, under the supervision of the probation service, committed murder, manslaughter, rape or another serious violent or sexual offence."
She added: "The British Government needs to admit it was wrong and commit to renationalising the probation service."
Ms Saville Roberts said this should include responsibility over justice in Wales being devolved to the Welsh Government.
Mr Gyimah, in his response to the written question, said: "A mandatory serious further offence review is triggered where an offender under statutory probation supervision is charged with murder, manslaughter, rape or certain other serious violent or sexual offences.
"Not in all cases will the charge result in a conviction for an SFO."
A Ministry of Justice spokesman said: "In 2014, we reformed our approach to probation so that for the first time ever, all offenders given a custodial sentence receive probation support and supervision on release.
"It is therefore misleading to compare the number of Serious Further Offences prior to our reforms with subsequent figures, as the number of people on probation is now significantly higher than before.
"A thorough investigation is always carried out when someone commits a serious further offence to see whether anything could have been done differently."