Private schools should be celebrated and not blamed for the "social ills" of the nation, a leading headteacher is warning.

There should be "collective pride" that Britain has created some of the best schools in the world, according to Richard Harman, chairman of the Headmasters' and Headmistresses' Conference (HMC).

In a speech, he is expected to argue that independent schools help to improve social mobility, not hamper it.

Private schools should not be lectured, he warns, especially by those who have benefited from this type of education - a comment that is likely to be seen as aimed at many leading politicians.

Mr Harman, who is also headmaster of Uppingham School in Rutland, is expected to tell the HMC's annual meeting in Newport, Wales: "It is time to stop scapegoating and start celebrating our schools and their contribution.

"Stop using them as lazy shorthand for the social ills of our country.

"Move beyond envy and take collective pride in the fact that a small country like Britain has created some of the very best schools in the world.

"Quite apart from the parents in the UK who are making real sacrifices to send their children to our schools, there are also parents from Azerbaijan to Germany to China and beyond, looking to get the best education for their child in this country."

Parents choose to send their child to a UK independent school firstly because of their academic excellence, Mr Harman is to argue.

Universities depend on the private sector for a strong supply of candidates for subjects such as science, engineering, medicine, languages and the classics, he is to insist.

Fee-paying schools also teach pupils other key qualities that are not measures in league tables, such as character, creativity and critical thinking, Mr Harman adds, as well as having a positive economic impact.

"Independent school leaders, along with many others, may be concerned by what one journalist recently called the UK's sclerotic social mobility," he is expected to say.

"This disease does not just affect the UK, of course, but attacking the excellence of the education we provide will never help solve it."

Mr Harman is due to tell the conference: "We raise our voices and say 'recognise our contribution'.

"We are and want to continue to be part of the solution to this country's and the world's challenges.

"We descend from veritable powerhouses of charitable enterprise like the Victorian public schools, many founded before there was any state education system at all.

"We have powerful charitable instincts and a desire to share excellence and best practice wherever we can.

"But don't lecture us, especially when there is much more important work to do in other areas of the education system and especially when many of you who do so have yourselves benefited from or use the service we provide. Hypocrisy is out of tune with the times."

Mr Harman is expected to use his speech to attack a suggestion made by former education secretary Michael Gove earlier this year that there would be no-one better to inspect private schools than Ofsted chief Sir Michael Wilshaw, and to call for exams regulator Ofqual to do more to improve the exams system, including marking.

Ofqual published a review of marking earlier this year, making a number of recommendations which it said would improve the quality of the system.

Mr Harman is also due to announce that the HMC is launching a new teacher training scheme in partnership with the private Buckingham University,

"Many good people have left teaching because they found themselves spending so much of their time filling in paperwork and trying to hit narrow, sterile performance targets, missing the bigger picture," he is to say.

"We want to keep good people in teaching by inviting them to work in schools where these things do not predominate."