A set of six stamps honouring some of the UK's greatest humanitarians has been released by Royal Mail.

The stamps, available from 8000 post office branches, commemorate the achievements of half a dozen people whose work improved the lives of others.

Nobel Prize-winning scientist Lord John Boyd Orr, the Ayrshire-born physician and biologist who advocated improved nutrition and global food provision, is one of those honoured in the set.

Sir John was the first director-general of the United Nations Food and Agriculture Organisation and co-founded the World Academy of Art and Science.

A Glasgow University graduate, he served as a medical officer during the First World War. Returning to Britain, he led research into diet and nutrition, and campaigned for improving people's diets.

When he received the Nobel Peace Prize in 1949, he gave the financial award to organisations devoted to world peace and a united world government.

Sir John was rector of Glasgow University from 1945 to 1947, later having a building named in his honour.

His grandson, Andrew Lubbock, said: "My grandfather was a most remarkable man.

"First and foremost, he was a great humanitarian and it is entirely appropriate that Royal Mail should make a stamp in his honour and it should be congratulated for doing so.

"I want to say thank you from myself, my family and the entire country for honouring an entirely honourable man."

Also appearing on the stamps is Sir Nicholas Winton, dubbed Britain's Schindler for saving the lives of Jewish children during the Holocaust.

Sir Nicholas, who died last year aged 106, organised eight trains to carry 669 children from Nazi-occupied Czechoslovakia to London in 1939, fearing they would otherwise be sent to concentration camps.

He also helped to find foster families for the children once they arrived in England but did not reveal his astonishing bravery for half a century, even to his wife.

Quaker philanthropist Joseph Rowntree, who used half his wealth to set up three trusts; Sue Ryder, who founded care homes for those in need in the UK and Europe; Eglantyne Jebb, a social reformer and founder of the organisation that became Save the Children, and Josephine Butler, who campaigned for women's rights and social reform, complete the collection.

Stephen Agar, from Royal Mail, said: "These six British individuals remain inspirational for their actions and achievements across nearly 150 years.

"It is timely that Royal Mail pays tribute to their humanitarianism with these stamps."