Stephen Lewis, who was in Dublin this week to mark World Aids Day, claimed that the battle against the spread of HIV was being "compromised" by the Vatican's anti-condom stance. He called on church leaders in Ireland and Europe to press the Vatican to change its policy.

"It is not helpful for the church to be so antagonistic towards condoms because condoms are the best single intervention we have, " he told the Sunday Tribune. "If the Vatican opens the door slightly then I think national [church] leadership everywhere should show the strength in voice and courage to say that the idea is to save lives and stop disease and so in that context condom use is morally justifiable and acceptable in church teachings."

Lewis was in Dublin to address Professor Michael J Kelly's inaugural lecture on HIV/Aids on Friday. He said it was important that the church began to view condoms as life-saving items, not merely contraceptives. The Vatican is conducting an internal review of policy on contraceptives and Lewis expressed his hope that its policy may be about to change.

The former leader of the Ontario New Democratic Party met with Taoiseach Bertie Ahern on Friday morning and expressed his delight at the work being carried out by the government's overseas aid agency, Irish Aid, especially in Aids-ravaged Lesotho and Mozambique, where Irish government money is used in conjunction with the Clinton Foundation to support communities affected by the Aids virus.

"I am extremely impressed by the extraordinary investment Ireland has made in Lesotho and Mozambique, " he said. "It is one of the most encouraging investments any western country has made. I think what Irish Aid has done in Lesotho is, frankly, astonishing. Ireland has shown that you can really change a country's fate if you move in to support it."

Irish Aid recently increased its annual budget to 813m, an increase of 130m. Ireland's contribution to the developing world now stands at 0.5% of GNP and is on target to rise to 0.7% by 2012.

However, while Lewis praised Ireland's contribution to the battle against Aids, he criticised the response of other leading industrialised powers, claiming that G8 leaders are more interested in photo opportunities than solving Africa's problems.

"The western world continues to betray the promises it made at the Gleneagles summit in 2005, " he said. "We won't have the money that Blair and Brown thought we would have; the countries who were promised debt relief in full have still not had it; and the trade talks, which were supposed to be the way we would reverse the economic stagnation of Africa, collapsed completely."

Referring to the Aids crisis as "the biggest health crisis in human history", Lewis warned that over 100 million people will have died from the disease by the year 2030 unless major steps are taken by the developed world.

Already 25 million people have died from Aids, but Lewis claims that the issue will be given the attention it deserves only when it makes major inroads into Europe and North America.

As it stands, fewer than 5% of infected children in Africa are receiving the treatment they need to keep them alive, while only 9% of HIV-positive pregnant women receive the drugs that would prevent the transmission of the virus from mother to child at birth.

"There is no precedent [to the Aids crisis], " he said. "There is nothing to equal it, not even the black death of the 14th century, with which comparisons are sometimes made. This is a health crisis like no other and our response internationally has been woefully inadequate."