Optician had been undertaking charity work in Nigeria

The British worker killed by militants in Nigeria was in the country to undertake charity work, it has been revealed.

Ian Squire, an optician, founded the Christian charity Mission for Vision in 2003.

He organised teams to take glasses to remote areas in Africa from donations to his opticians' surgery in Shepperton, Surrey.

Squire was killed while working in the rural Delta area of the country.

Three others who were kidnapped, Alanna Carson, David Donovan and Shirley Donovan, have been released.

A Foreign and Commonwealth Office (FCO) spokesman said the Nigerian authorities were investigating the kidnapping, saying it had been a "traumatic time" for those involved.

"Our staff will continue to do all we can to support the families," said the spokesman.

It is understood the four were taken when raiders stormed a rural community they were living in within the Delta area.

The FCO currently advises against all but essential travel to much of Delta state, saying there is a "high threat of criminal kidnap".