More than 160 prisoners convicted of terror offences have been released early over the last seven years, according to a former security minister.
Conservative John Hayes said he was "surprised and disappointed" by the "significant" numbers contained within research compiled by the House of Commons Library.
He added this figure did not include those offenders who had served fewer than 12 months behind bars.
Mr Hayes disclosed the data as he supported the Government's Terrorist Offenders (Restriction of Early Release) Bill.
The legislation aims to prevent automatic release from prison of terrorist offenders halfway through their sentences, following the terror attacks at London Bridge and in Streatham, south London, by convicted terrorists Usman Khan and Sudesh Amman.
Speaking in the Commons, Mr Hayes said: "I consulted the House of Commons Library, as good members of this House do, and was surprised and disappointed to find that since 2013 something like 163 convicted terrorists have been released early.
"I excluded from my considerations anyone who'd been serving a sentence of less than a year.
"Those are just people serving a sentence somewhere between 12 months and more than four years.
"So leaving aside the short sentences, the more serious terrorist prisoners have been released in significant numbers.
"Just imagine the effect on our security services and police of having to deal with the possible consequences of those releases.”
Mr Hayes said he expected some of the people released would have been rehabilitated and de-radicalised.
He added: "But we know that's not always the case.”
Emergency legislation to prevent the automatic release from prison of terrorist offenders halfway through their sentences moved closer to becoming law on Wednesday.
MPs allowed the Terrorist Offenders (Restriction of Early Release) Bill to clear all its Commons stages on Wednesday and it will now progress to the Lords for further scrutiny.
Ministers want to get legislation on the statute book by 27 February, before the next terrorist prisoner comes up for release.
It follows the Streatham terror attack earlier this month, when Sudesh Amman stabbed two bystanders with a knife he had grabbed from a shop.
The 20-year-old was jailed in December 2018 for possessing and distributing terrorist documents but had been freed midway through his sentence less than a fortnight earlier.
It was the second attack in three months to be carried out by a convicted terrorist, after Usman Khan stabbed and killed two people at Fishmongers' Hall near London Bridge in November.
He had been released nearly a year earlier, halfway through a 16-year jail sentence.