The forced deportation of a Cameroonian playwright and her husband, scheduled for Saturday, is "disturbing, shocking and unjust", the actor Juliet Stevenson has said. The actor joined campaigners including writers Joan Bakewell and Andrea Levy in condemning the UK Border Agency (UKBA), which they say has disregarded its own procedures.

Lydia Besong – who has written three plays since coming to the UK in 2006 – was not in her Manchester house when it was raided at dawn on Monday, but her husband, Bernard Batey, was taken and detained at the Colnbrook removal centre near Heathrow airport. Besong has gone into hiding, with the couple scheduled to fly to Cameroon at 8pm on Saturday.

The couple had filed a fresh, joint asylum claim with new evidence given to UKBA in July, but were not told it had been rejected before their house was raided. UKBA documents, later faxed to the couple's lawyer, reveal that the decision to refuse further submissions was taken on 17 August.

The couple have also been supported by Ali Smith, Sarah Waters, Lisa Appignanesi, Linda Grant and the writers' group English Pen.

Stevenson, who hosted the first production of Besong's play How I Became An Asylum Seeker, said the playwright was a "remarkable" woman. "It is just appalling. Lydia Besong is an incredibly courageous woman who has been imprisoned and raped in her own country and then has put her head above the parapet to talk about her experience and write her plays. To snatch her without giving her time to prepare a defence is legally indefensible and humanly abusive and unjust," she said. The play was put on by Women for Refugee Women in London.

Bakewell said: "Officers arriving at 7am does smack of bullying, and I don't like that." In a letter to the immigration minister, Damian Green, urging him to consider the case she wrote: "As concerns about differing loyalties in Libya make the headlines, protesters such as Lydia Besong from Cameroon need to be heard. Perhaps in years to come they may be leaders of some Cameroon 'spring' and in a position to judge how they were treated by Her Majesty's government." The couple say they were jailed and tortured in Cameroon as punishment for involvement with the SCNC pressure group which campaigns for southern Cameroon's independence. While in jail, Besong was raped by a guard, she said.

The pair believe their lives would be in danger if they returned to Cameroon, especially after Besong's play garnered negative media coverage in Cameroon.The human rights organisation Rapar said UKBA's action contravened its own procedures. "We are shocked at the behaviour of the UKBA. They have known about this decision for almost a month but have failed to inform Lydia and Bernard, or their lawyer," it said.

An Amnesty International report in May confirmed that the regime of President Paul Biya continues to persecute the SCNC. "Lydia and Bernard will be in grave danger if they are returned to Cameroon," said Grant.

UKBA said: "Decisions not to inform applicants of the outcome of their representations in advance will be taken where we believe individuals may deliberately seek to frustrate or delay the removal process."

Speaking from an undisclosed location Lydia Besong said she feared for her life and that of her husband. "We are members of the SCNC in Cameroon. We have been targeted and put in detention. When the UKBA came for us on Monday it was like when [the government] came for us in Cameroon. I thought we would be safe in the UK. I did not think we would be put in a situation where I am not safe to go home."

The English literature graduate, who was a teacher in Cameroon, said writing plays in the UK had been a positive experience for her, but had put her in further danger. "Many people have opinions about asylum seekers and I hope my play helped them see that we are people and give them the truth. If I get sent back to Cameroon I will not be able to write any longer. I will be persecuted."