The government is under pressure from MPs and charities to relax family reunion rules for refugees settled in the UK.

Current immigration rules only allow adult refugees to apply for their married or civil partners and dependent children under 18 to join them. Grandparents, parents, siblings and children who are 18 or older are ineligible.

In addition, children who are in the UK alone and have refugee status do not have a right to be reunited with even their closest family members.

MPs and campaigners want the rules to be changed, either through amendments to the government’s flagship post-Brexit immigration bill or through a private member’s bill put forward by the SNP MP Angus MacNeil.

This week, Oxfam will call on its supporters to step up pressure on ministers by contacting their MPs and supporting the changes.

It will say: “In 2019, we’re going to need to keep making our voices heard, pushing for changes that would make a real difference to people’s lives. Children are still being forced to grow up alone, young women are stranded in war zones, and elderly parents are being left to fend for themselves. But things can change if we work together to help keep families together.

“We’ve been keeping up the pressure, asking the government to make sure the bill is granted proper time for debate so it can progress through parliament. We’re hoping it will progress to the next stage in the coming months. There may also be opportunities for MPs to introduce these changes as part of the immigration bill. Now we need another big push to ensure as many MPs as possible come out in support of refugee family reunion.”

Last week the immigration bill was debated in the House of Commons and numerous MPs raised the issue of family reunion.

Stuart McDonald, the SNP’s spokesman for immigration, told the Commons: “The UK is once more an outlier in terms of the refugee family reunion rules it has in place. Sadly, the [immigration] bill does not mention asylum at all, and gives us little chance to address those issues.”

Afzal Khan, the shadow immigration minister, said: “We find the bill a missed opportunity to address the moral and humanitarian failures of this Tory government towards refugees and asylum seekers… There is nothing ​in the bill, and very little in the white paper, on refugees and asylum seekers. At a minimum, we must bring an end to indefinite detention and fix refugee family reunion.”

The home secretary, Sajid Javid, said it was “right that we constantly review the rules to make sure that they continue to be fair at all times”.