Refugees are struggling to integrate into British life because of restrictions on bringing their relatives to the country, campaigners claim.
Oxfam and the Refugee Council called on the Government to amend the rules, labelling them "unfair" and "restrictive".
The organisations said many refugees are plagued by worry about loved ones who are still overseas - leaving them unable to focus on finding work, making friends or learning English.
Maurice Wren (pictured), chief executive of the Refugee Council, said: "The evidence is clear: reuniting refugee families gives them the best chance of living settled and fulfilling lives.
"Denying them the chance to restore their family ties condemns them to a future of anguish and guilt, with the anxiety of separation undermining their mental health.
"We urge the Government to do better by refugees and amend the unfair, restrictive UK rules that prevent refugee families from being reunited just when they need each other the most."
Partners, spouses or children aged under 18 can apply to join those granted humanitarian protection or asylum status in the UK.
In a research paper, Oxfam and the Refugee Council recommended expanding the criteria for who qualifies as a "family member" in refugee cases.
Researchers examined the experiences of 44 families from countries including Syria, Iraq and Somalia.
The report said 33 of the families were unable to focus on activities essential to integration, such as learning English, because they were preoccupied with worries about family members, experiencing feelings of guilt or struggling with mental health problems.
In 11 cases refugees have now been reunited in the UK with some of the loved ones they left behind, and for nine of those integration into British society was "quicker and easier" as a result, according to the study.
Sally Copley, head of policy, programmes and campaigns at Oxfam, said: "Refugees want to be able to play an active role in their communities and be able to learn English, but all too often they face pointless hurdles because of a system that keeps them separated from their family.
"This in turn destroys their confidence to go out, make friends and be part of their community. As this study shows, it is not only harmful but also damaging to their chances of integrating successfully."
A Home Office spokeswoman said: "We support the principle of family unity and have reunited over 24,000 families in the last five years.
"The routes already in place in the immigration rules allow extended family members lawfully resident here to sponsor children where there are serious and compelling circumstances.
"Extended family are also able to come here in exceptional circumstances."
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