The warning coincides with the release today of the 2009 epidemic report from the World Health Organisation and the Joint UN Programme on HIV/AIDS, which estimates that the number of people living with HIV in the UK has doubled since 2000 to 73,000.
The two organisations say an estimated 33.4 million are infected with the virus worldwide, up from 33 million in 2007. The rise has been attributed to improved access to antiretroviral drugs that are stopping HIV sufferers from dying.
In spite of significant medical advancements in treating the virus over the last thirty years, Tearfund said stigma remained "one of the greatest barriers to successfully changing the story of the Aids pandemic".
"It is devastating that almost three decades after HIV was first identified, stigma and ignorance are thriving, both here in the UK and overseas," it said.
Tearfund said that although the church could be very effective way of mobilising communities to end stigma and improve quality of care and access to treatment, stigma was still present within its ranks.
"The church at its best can be a source of great hope and support to people living with or affected by HIV," it said.
"In our work across the world, day in, day out we see church volunteers caring for orphans, the sick and bereaved, helping people get access to treatment and crucially, challenging stigma.
"But ignorance and prejudice remain within the church and until these harmful attitudes are completely let go of, the church's efforts will be undermined."
One Zimbabwean HIV sufferer now living in the UK told of painful encounters in churches here.
"After church services I would make tea and sandwiches for people. I noticed how some people would not take them, even the church leader," said the woman, who wished to remain anonymous.
"I was holding a lady's newborn baby at church and congratulating her. You know, they are so beautiful that you are tempted to kiss them. But she took the baby away from me. And I broke down and cried. I thought, Lord forgive them, for they know not what they do."
In Uganda, HIV sufferer and specialist at Mildmay Hospital Dr Stephen Watiti said stigma often prevented people from seeking treatment, particularly if they were Christian.
"When religious leaders come for treatment some don't put on the dog collar. Religious people find it very difficult to register for treatment using their own names. They don't want to be known as HIV positive," he said.
WHO and UNAIDS estimates that the number of people dying from HIV has dropped by 10 per cent in the last five years as a result of greater access to antiretroviral drugs, while HIV prevention programmes have cut the number of people contracting the virus by 17 per cent.
Tearfund's Veena O'Sullivan warned, however, that the church could not afford to be complacent.
"There is no room for complacency and stigma in the fight against HIV and Aids," she said. "For every three people who access treatment, five people are newly infected. We take two steps forward and one step back. The church, with its reach and influence, can and must do more to change the face of the Aids pandemic."