The pair were meant to join Unicef officials to take part in a polio immunisation programme, but security concerns following the death of 12 people, including the town's mayor, in the blast on September 11 persuaded officials to axe the four-day trip, which was supposed to start on Friday.

"Since the bomb in Jaffna, we have been monitoring the situation and we decided that we were not sufficiently confident it was safe enough for them to go," said Unicef's representative in South Africa, Colin Glennie.

Military officials in the area blamed the bomb on Tamil Tiger rebels fighting government troops for a homeland for minority Tamils.

Robbie Williams: Moving to safer town

Now the duo are to visit the northern frontier town of Vavuniya to take part in the immunisation programme. They will also visit a refugee camp there.

"It's a much safer place for them to go, as it's in the middle of the country and away from the fighting in the north. They'll see the same kind of work going on there as they would have done in Jaffna," said a Unicef spokeswoman in London.

Dury suffered from polio as a child, and travelled to Sri Lanka last year with Unicef, and has made the trip this year despite his battle with cancer.

Since his pop heyday with hits such as Hit Me With Your Rhythm Stick in the late 1970s he has diversified into acting as well as music.

Former Take That heart-throb Williams became involved with the campaign after meeting Dury earlier this year.

Unicef officials say 95% of children have been immunised against polio. The organisation aims to eradicate polio in Sri Lanka by the year 2000.