Rishi Sunak insisted he had reformed the asylum system “every which way I can” amid questions over how a sex offender suspected of carrying out a chemical attack remained in the UK.

The Government had already taken action to stop people trying to “game the system”, Downing Street said, as pressure mounted on ministers to explain how Abdul Ezedi was allowed to stay in the country years after being convicted of sexual assault and exposure.

Home Secretary James Cleverly is understood to have asked for the facts of Ezedi’s case as he examines whether there are flaws in the asylum system and considers whether changes to the rules need to be made.

Police have been hunting for the on-the-run Ezedi since a 31-year-old woman and her daughters, aged eight and three, were attacked in Clapham, south London, with what officers believe was a “very strong concentrated corrosive substance” – thought to be alkaline – on Wednesday evening.

The Home Office twice rejected 35-year-old Ezedi’s asylum claims but his application was later granted by a judge on appeal, according to Government sources.

The Prime Minister dodged questions on whether the Government should close a “loophole” in the immigration system amid suggestions asylum seekers are converting to Christianity to secure leave to remain in Britain.

It comes as Dave Rees, an elder at a Dorset church, said 40 asylum seekers on the Bibby Stockholm barge had come forward to become Christians.

Asked whether changes need to be made, Mr Sunak told broadcasters on Monday: “I’ve been very clear that, when it comes to illegal migrants, we need to have a system where someone who comes here illegally should not be able to stay.”

Asked whether there is a “loophole” that needs to be closed, he said: “More generally I’ve tightened up the system every which way I can, but fundamentally this is just about fairness. People coming here illegally at that point shouldn’t be able to stay.”

Downing Street later stressed the Government had already taken action to stop people trying to “game the system” with legal reforms as the Prime Minister’s official spokesman said while the UK had a “proud history of welcoming people who are genuinely fleeing religious persecution”, it would not “tolerate people taking advantage of this”.

Cabinet minister Chris Heaton-Harris told LBC that Ezedi would have been detained and deported if the Government’s Nationality and Borders Act – which became law in 2022 – had been in place, adding: “We’ve tightened our laws since.”

Ezedi, believed to be from Afghanistan, is understood to have arrived in the UK in 2016, reportedly in the back of a lorry.

He avoided jail after pleading guilty to charges of sexual assault and exposure, instead being placed on the sex offender register for 10 years when he was handed a suspended sentence at Newcastle Crown Court on January 9 2018, according to the Crown Prosecution Service.

Foreign national offenders currently only qualify for deportation if they are sentenced to – or have served – an immediate custodial sentence of 12 months or more under Home Office rules.

Ezedi’s asylum claims are understood to have been twice rejected by the Home Office, shortly after he came to the UK in 2016 but also in the wake of his prosecution in 2018.

He challenged the Home Office’s decision to refuse him asylum by successfully lodging an appeal with the First-tier Tribunal (Immigration and Asylum Chamber), which was granted by a judge in October 2020, according to Government sources.

Ezedi was apparently permitted to stay in the country after a priest confirmed he had converted to Christianity and was reportedly “wholly committed” to his new religion. The priest in question was not Roman Catholic or from the Church of England, it is understood.

The Home Office can apply to the Upper Tribunal to appeal against court rulings in asylum cases, but it is so far unclear whether the department did so in this case and was unsuccessful.

Court documents detailing such rulings are confidential and can only be disclosed to the media or published with permission from a judge.

Refugee charity Action Foundation based at the evangelical City Church in Newcastle confirmed it supported Ezedi between April 29 2021 to March 2 2022. The church offers Alpha courses – an introduction to the basics of Christianity used by those converting to the faith.

An Action Foundation spokeswoman said: “We’d like to express our heartfelt sympathy to all the people injured in last week’s attack and hope that Ezedi can be apprehended soon. We utterly condemn violence against women and children.

“Our charity last had contact with this man almost two years ago when he left one of our lettings properties in Newcastle which he had occupied for the previous 10 months. We understand he then moved on to other homeless accommodation in the city.”

When discussing asylum seekers on the Bibby Stockholm barge, Mr Rees, whose name appears listed as an elder on the Weymouth Baptist Church website, told the BBC Radio Four Sunday programme that there is a “rigorous process” in place for conversions, with a Farsi-speaking minister helping.

There’s no reason we would doubt these asylum seekers from their profession of faith

He said he was “confident” in the measures and scrutiny in place, adding: “There’s no reason we would doubt these asylum seekers from their profession of faith.”

Some people were Christians in their own country and others had taken part in Alpha courses in the UK, he said as he explained what questions they face to confirm their faith.

He said: “Obviously we need to make sure that they believe in Jesus, they believe in the Father, Son and the Holy Spirit, they repent of their sins, and also they want to start a new life in the church.

“So those are the sort of questions that we asked them and they have to give a public testimony at their baptism, which they did in their native language, and was translated into English. And there was no qualms at all about the content of that testimony, which was clear and conclusive about their faith in Jesus Christ.”

Pressed on whether that has been true in every case he had been involved with, he replied: “In every single case we’ve dealt with, yes, it has been very true, yes.”