The quality of teaching in England's schools is better than ever and the overall standard of education is improving, Mike Tomlinson, head of the education watchdog, reported.

The number of lessons judged to be good, very good or excellent has risen over the past year, the Office for Standards in Education's annual report - published on Tuesday - showed.

And more schools than ever have no unsatisfactory lessons, the Ofsted report says.

Ofsted chief Mike Tomlinson: Quality improvement

But Mr Tomlinson also highlighted the problem of teacher shortages and warned that the situation could jeopardise the rise in standards.

He expressed concern about the growing trend - in some parts of the country and in some shortage subjects - of teachers taking lessons in subjects which were out of their specialist field.

"What we're also seeing - and the report makes clear - is that more and more supply teachers are being used than previously and than some head teachers would want to use," Mr Tomlinson told BBC Radio 4's Today programme.

Key Stage 3

The chief inspector also raised some concerns about lessons for 11 to 14 year olds, especially in literacy and numeracy.

Mr Tomlinson is very concerned about the educational performance of disadvantaged groups, especially boys from some ethnic minorities.

He warned that African-Caribbean, Pakistani and Bangladeshi boys were not benefiting from the advances in the education system.

Parental responsibility

Mr Tomlinson said parents could play a greater role in helping schools raise standards and should support school in the application of codes of discipline.

It really is important that parents... support the school in its wish to have sensible good behaviour around the school

Mike Tomlinson

"It's impossible for teachers to impose such codes if parents will not support them," he said.

The Liberal Democrat's education spokesman, Phil Willis, praised Mr Tomlinson for highlighting the number of children being taught by "out-of-field" teachers.

"Once again, I call upon the government to conduct a secondary staffing and curriculum survey.

"It is the only way to understand the depth of the problem and plan teacher supply effectively in the longer term," he said.