In 2009, 1,060 prisoners successfully completed 1,775 courses, almost double the number achieved in 2007, the figures show.

The interest for adult further education has grown continuously in recent years and it is especially courses at tertiary and high-school level that have grown in popularity. Swedish for immigrants (SFI) courses have also experienced a boom in demand.

It is not just the number of grades and students which is so positive, the standards are also high, the service said.

“We maintain a very high level of quality. Quality and offering the possibility for everybody to study have always been top priorities,” said Lena Axelsson, head of education at the service, in a statement on Wednesday.

Axelsson pointed out that grades awarded by the prisons service are worth as much as those issued by other educational establishments in society.

“The prisons service operates according to the same laws and conditions as all schools in society and the schools inspection monitors our operations,” she said.

The service also pointed out in its statement that grades issued by the prisons service do not state where they have been issued.

The Swedish Prison and Probation Service (Kriminalvården) employs 125 teachers at its facilities across the country.