Professor Neville Bennett, who is directing the project along with Elizabeth Smith, said: “The message from early-years educators is that play is the bedrock of practice.

“But when you actually look at play in reception classes - because that is where most of the nation’s four-year-olds are - it tends to be a time-filler or a bit of a reward after you have finished some work.”

A body of research looking at both pre-school and infant settings has shown that play is “typically limited, lacking in cognitive challenge, poorly integrated into the curriculum and often lacking in adult support,” Professor Bennett said.

The Exeter project, funded by the Economic and Social Research Council, hopes to identify what is causing the problem and to highlight good practice by working with a group of successful teachers.

The researchers then hope for further funding to develop ways of improving practice among teachers.

Both Labour and the Conservatives are pushing to increase quantity of provision for young children, Professor Bennett said. “We are saying that’s good, but we have got to be clear about quality.”