Home secretary Theresa May is coming under growing pressure over an apparently botched attempt to deport a seriously ill man from Britain on a private plane.

Isa Muazu, who was carried to the plane on a stretcher after a 90-day hunger strike, was returned to the UK after a 20-hour flight that saw the plane prevented from entering Nigerian airspace.

On Sunday evening Labour joined a growing chorus of voices calling on May to explain her actions, saying the deportation had been carried out without humanity or compassion.

"Theresa May needs to explain how this case has been handled," shadow immigration minister David Hanson said. "How could the Home Office put a man in this medical condition on a long flight at taxpayers' expense with no agreement from anyone that the plane could actually land? Deportations should be carried out with competence and humanity. Neither of those things seem to have happened in this case."

Hanson's comments come after weeks of campaigning by human rights groups, celebrities and parliamentarians.

Muazu's supporters say he was near death when he was forcibly removed on Friday and said he had been caught up in "political point scoring" by the government.

On Sunday Liberal Democrat MP Julian Huppert described the case as shocking and said he would be tabling an urgent question in the Commons.

Lord Roberts, a Liberal Democrat peer, said that although he was delighted that Muazu was back in the UK, he was horrified the UK authorities had tried to remove him in the first place.

"I saw him on Tuesday," he told the Observer. "Goodness knows what state he must be in now. Theresa May must consider her role immediately. She caused immense damage to one individual and spent an extraordinary amount of taxpayers' money."

It is understood the Home Office spent between £95,000 and £180,000 on the flight, after a previous deportation attempt on a scheduled Virgin Atlantic flight was cancelled.

Muazu says he is terrified of being sent back to Nigeria after defying the terror group Boko Haram by refusing to join their ranks. His case has been backed by numerous politicians, celebrities, playwrights and human rights groups who have written to May to appeal on his behalf.

Nancy Maller, who helped organise a vigil for Muazu outside the Home Office last week, on Sunday described the government's actions as "disgusting".

"It is clear to anyone with an ounce of humanity that after nearly 100 days of a hunger strike that Ifa Muazu is on death's door and too unwell to be locked up in an immigration detention centre or forcibly deported to Nigeria. This is just one example of the inhumane asylum system that we have in this country, and shows how far this government is willing to go to score political points. It brings shame on this government and on this country."

A spokeswoman for the Home Office said it did not comment on individual cases.

• This article was amended on 5 December 2013 to correct the spelling of Isa Muazu's name, from Isa Muaza as the original said.