by Nic Rigby BBC News Online, Norwich

Pemba Island is described as an "island paradise"

Grace Forster, 18, from Whittlesey, Cambridgeshire, and a man also thought to be about 18, were treated in hospital in Dar es Salaam.

Conservation group Frontier, which organised the trip, said one of the victims had been discharged and the second was expected to be on Sunday.

Friday's attack on the island of Pemba took place at about 7.30pm local time.

Seven attackers armed with guns and machete knives stole Frontier's boat and engines, as well as money and personal possessions, group spokesman William Hedley-Miller said in a statement.

The bullet entered Grace's left side and travelled through just missing her spine - it could have ended her life Ian Forster, father of Grace

Ian Forster, the father of Grace, said: "The bullet entered Grace's left side and travelled through just missing her spine - it could have ended her life."

He said both victims were expected to be flown back to the UK within a couple of days.

Mr Forster said he hoped Frontier would look into security issues.

"This needs to be thoroughly checked out," he said.

"My concern as a parent is what are they going to do to stop the same thing happening again."

He said he was also concerned that the group's other 23 volunteers should be getting counselling.

Mr Hedley-Miller said the other volunteers had been moved from the island, parents had been informed, and senior Frontier reperesentatives were flying to Tanzania to help.