Image copyright Thinkstock Image caption In the US, selling downloads of lessons has been lucrative for some teachers

Teachers in the UK, who have often complained about long hours at home making their own class materials, are selling their lessons online.

The TES website is running a digital marketplace for teachers to sell their lesson ideas to other teachers.

It is the latest example of teachers producing their own bespoke classroom materials and sharing them online.

Earlier this year, a school in Cambridge published its own set of GCSE textbooks on Apple's iBooks.

The website of TES Global - formerly The Times Educational Supplement - is offering teachers a digital platform to make money out of their lesson plans and teaching materials.

Ideas for sale

The idea of teachers sharing ideas and materials for lessons online has expanded rapidly, with up to a million downloads per day of free material through the TES website.

But there is a move to commercialise this, with teachers able to put a price tag on their lesson ideas.

There are about 3,000 teaching materials on sale so far, such as material for primary science and poetry for £1 and resources on food technology and physics for £2. These are accompanied by teachers' reviews and ratings.

There is already an established commercial market in the US, with websites turning a handful of teachers into millionaires with particularly popular downloads.

Head teachers' leader Brian Lightman said it reflected the "pace of change" when online information can be shared so quickly and when teachers were under pressure to be "agile" in providing up-to-date materials.

But he cautioned: "Teachers need to be careful before they sell resources, if they're employed in a school there is a question about intellectual property and schools need to have a clear protocol."

Mr Lightman, general secretary of the ASCL head teachers' union, sees this trading in lessons as part of a wider trend for teachers to take charge of their professional lives and produce the materials that they need.

The Stephen Perse Foundation, an independent school in Cambridge, has pioneered the production of its own digital textbooks, which are available free for any other schools to download online.

Rob Grimshaw, chief operating officer of TES Global, described the marketplace as an "important milestone" for online school resources.