The Office for Standards in Education has joined one of the most contentious debates in education by calling for schools to spend more time teaching the history of the British Empire.

Ofsted says secondaries are not spending enough time on the subject in an intervention which will hearten traditionalists, who call for the empire to be celebrated, and progressives, who want pupils to be taught about our post-colonial heritage.

However, teachers say that the curriculum is too crowded to devote much time to the subject, despite its 500-year influence on the nation.

The inspectors’ comments came at a conference on the teaching of conflicting interpretations of history, using the subject of empire as a centre-point.

Scott Harrison, the subject adviser for history, told The TES that in some cases teaching could amount to one lesson during the three years of key stage 3, and virtually nothing at GCSE.

He said: “Is devoting, typically, a lesson on empire in a three-year history course sufficient given the subject’s significance? I have to say it is not sufficient.”

At KS3, the national curriculum says one of the six units should be on Britain 1750-1900. But this area of study does not focus exclusively on the empire.

There is also one British unit covering slavery. This would touch on the empire, but mean some pupils might see the era mainly in negative terms, said Mr Harrison.

Last summer, Professor Niall Ferguson, the New York university history don and TV academic, made a plea for the empire to become the main organising theme of secondary history study.

The Schools History Project last month launched a textbook, The Impact of Empire, aimed at secondaries wanting to educate their pupils about the varying academic and popular accounts of the subject.

There are a number of analyses of why the subject may have been neglected in classrooms.

Katherine Hann of the British Empire and Commonwealth Museum in Bristol, where the conference was held, said there had been public “awkwardness and embarrassment” about our imperial past until the 1990s. This, though, was changing.

Gary Clemitshaw, a teacher educator from Sheffield university, said: “A generation of teachers at work in schools from the 1960s welcomed decolonisation and the end of the empire, and have therefore wanted to turn away from it and emphasise other things. But in doing that, they have ignored an area which is central to historical understanding.”

But if there is growing acceptance that the subject merits more attention, two factors appear to stand in the way. First, many history teachers believe that the emphasis on the empire should not simply mean celebrating its achievements.

Second, they are concerned that the curriculum is too crowded to teach it properly. Sally Duckett, a history teacher at the Ridings high, Winterbourne, Bristol, said the school had had to cut the number of lessons on the empire from six to three because of the advent of citizenship in recent years.

She said: “I think we should do more on the empire, and I will bring it up when I go back to school. But it will be seen as just another thing to do.”

COGS IN THE MOTOR OF HISTORY

At key stage 3, the national curriculum says pupils should study history through six areas: Britain 1066-1500, 1500-1750 and 1750-1900 as well as a pre-1914 European study, and world studies pre-and post-1900.

Among 16 suggested topics in Britain 1750-1900 are the American Revolution, the slave trade and “the development of Empire and colonial rule in India, South-east Asia and Africa”.

There are 20 topics for study under “Britain 1500-1750”, including the voyage of the Pilgrim Fathers and the foundation and fortunes of the East India company.

Among 25 topics under “World studies after 1900”, one covers the break-up of the empires of European countries, another the growth of the Commonwealth.

Inspectors and history experts say the empire is little studied at KS2 and gets too little attention at GCSE.