Refugee children could be blocked from reuniting with their families in the UK after Brexit, the head of UNICEF UK has warned. 

The UK boss of the children’s charity Mike Penrose has called for an overhaul of UK immigration law to help keep children fleeing conflict safe after Britain leaves the EU. 

“Brexit could risk the ability to get children fleeing war and persecution to the safety of their close family in the UK,” Penrose told the Guardian. 

READ MORE: George and Amal Clooney are Sending Nearly 3,000 Syrian Refugee Children to School in Lebanon

“Now is the time for the UK government to broaden its own rules and ensure the protection of unaccompanied refugee children.” 

Currently, family reunification law allows unaccompanied minors to reunite with family members who can care for them in a host country, including a parent, an uncle or aunt, grandparents or older siblings.

That’s because they are currently covered by the EU’s “Dublin III” regulation, which includes a wider definition of what it means to be a “close relative,” – including adult relatives other than parents.

When the Calais camp was shut down last year, more than 500 children were reunited with family members in the UK under the “Dublin III” regulation, according to the Independent.

However, following Brexit, only the UK’s rules will apply. 

According to UK immigration law, an unaccompanied minor can only apply to be reunited with their parents. 

So if a child has been orphaned, following Brexit they won’t be able to apply to be reunited with other adult relatives that could care for them. 

READ MORE: 'There Are Many Other Kids Here': One Syrian Boy Tells His Story of Child Labour

Penrose has urged the UK government to expand the reunification law to prevent orphaned refugee children being left without an adult relative to care for them. 

He added: “By making small changes, the government can show, just as it did in Calais, that it is serious about ending the need for children to make dangerous journeys across the Mediterranean in order to reach their loved ones in the UK.”

The Refugee Council has also recommended that the government expands the criteria for qualifying family members for reunification, in a reportfrom February 2017.

Under the “Dublin III” regulation, an adult can only apply for family reunification with a spouse or a child.

READ MORE: UK Aid Makes Britain, and the World, a Safer Place

Plans for what the immigration system would look like after the UK leaves the EU will be revealed in a white paper this year, according to the government. 

A new immigration bill is set to go through parliament in 2018. 

A Home Office spokesperson told the Guardian it was too early to commit to changes, but “both the UK and our European allies have a clear interest in ensuring that our strong cooperation on asylum continues and strengthens after we leave the EU.”