On Sunday Emad Al Swealmeen detonated a suicide bomb in a taxi outside Liverpool Women’s Hospital. The attack took place just moments before the 11am two minutes silence on Remembrance Sunday.
Police said it could take “many weeks” before they fully understand what happened in terms of planning, preparation and how things unfolded.
It has since emerged the terror suspect moved to the UK from the Middle East several years ago.
Al Swealmeen was a Christian convert who had an asylum claim rejected in 2014.
While refusing to comment directly on the case of Al Swealmeen, speaking to journalists today, No10 said Mr Johnson admitted the UK’s approach to asylum seekers need to be “improved”.
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The Prime Minister’s official spokesman said more needed to be done to speed up the removal of those whose asylum claims are rejected.
He said: “In broad terms we want to take steps to speed up removal of those with no right to be in the UK and streamline appeals and judicial process that can be used to frustrate removal.
“This is one part of the UK’s new plan for immigration and remains the only credible plan to fix our broken asylum system.”
He added: “We think the approach needs to be improved.
“It’s something the Home Secretary is very focused on.”
In July of this year the Government introduced its Nationality and Borders Bill to Parliament.
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Officials say it seeks to make changes to the asylum process to “make the system fairer and more effective so that we can better protect and support those in genuine need”.
It also looks to introduce a new “‘one-stop’ process to ensure that asylum, human rights claims, and any other protection matters are made and considered together, ahead of any appeal hearing”.
The changes aim to prevent repeated last-minute claims which mean the asylum process can be dragged out for years after an initial rejection.
This morning Home Office minister Damian Hinds refused to comment on why the suspect had been allowed to stay in the country despite having been denied asylum.
He told Times Radio: “It is a live investigation and the police do have to have the space, the time, to be able to conduct that investigation fully and to carry on their searches of the key address and carry on with the analysis.”
Mr Hinds said it is “not impossible that there could be other people involved” and if that turns out to be the case, police will “make arrests quickly”.
Four men arrested under terrorism laws in the Kensington area of Liverpool – three aged 21, 26 and 29, who were held on Sunday, and a man aged 20 who was detained on Monday – have now been released from police custody following interviews.
The Police investigation into the bombing continues.