Teachers are bowing to pressure to make sure pupils pass exams and are being "forced to manipulate" results, a survey has suggested.

One teacher even admitting to re-writing their students' homework to match the marking criteria, while most staff cited pushy headteachers as the reason they adopted the unprofessional practices.

Many are turning to one-to-one lessons, after-school classes and even rewarding pupils in an effort to bump up grades. Teachers, who claim their integrity is as stake, are blaming Ofsted, parents and politicians for piling on the pressure and demanding better grades.

The poll, conducted by the Association of Teachers and Lecturers (ATL), found that almost three quarters (73.2%) of teachers feel under "a lot" of pressure to get pupils through tests and exams, with 70.6% saying this had increased in the past two years alone.

Nearly two thirds (63.9%) said they feel under more pressure now that 10 years ago.

There are fears that test pressure could affect teachers' professionalism, with almost two fifths (39.1%) saying it could be compromised.

More than a third (35.2%) said their integrity could be compromised, the poll, published as ATL meet for their annual conference in Manchester, found.

One primary school teacher in England told the survey: "I have been forced to manipulate results so that levels of progress stay up, as our head fears [there will be] an Ofsted inspection should our results waiver. I work in an infant school."

A one-to-one booster teacher at a secondary school in England said: "The school I work at definitely pushes the boundaries of exam integrity.

"Maintaining their 'gold-plated' status by far takes precedence over developing the abilities of the pupils. Controlled assessments and aspects of coursework are problem areas for cheating, with senior leadership driving the agenda."

And a teacher at a Northern Ireland grammar school said: "In some cases I end up virtually re-writing my students' homework to match the marking criteria, rather than teach them my subject, French. I do this because there is simply not time to do both!"

The vast majority of those surveyed (88.2%) said the pressure to achieve good results comes from their school leadership or management, followed by league tables and banding (65.9%), Ofsted (51.1%), parents (49.7%) and government (34.7%).

A third (33.3%) said they feel pressure from pupils, and nearly half (44.2%) said they place it on themselves.

The most popular way to help pupils to prepare for tests, outside of normal class work, was to supply more practice papers and questions than in previous years (cited by 71.2%).

Two fifths (41.5%) are helping pupils with coursework, while others lay on one-to-one tuition (63.2%), after-school classes (68.4%), weekend classes (9.1%) or offer rewards and incentives (25.7%).

Around a third (31.2%) say they attend meetings to find out exam themes, the poll, which questioned 512 teachers, revealed.

Teachers also raised concerns about the impact of exams on pupils, with most saying that testing is the biggest pressure on young people, ahead of other issues including bullying, family break-ups, financial problems at home and peer pressure.

Some 88.2% said the pressure of testing had a negative effect of having a broad curriculum, while 72.5% said it damaged the quality of teaching and 70.6% said it harmed learning.

A teacher at a state secondary school in England said: "Teaching to the test means that I am not prioritising the needs of the pupils in learning about my subject; it only prepares them to respond to formulaic questions."

ATL general secretary Dr Mary Bousted said the UK's children are still among the most tested in the world.

"This creates a huge pressure on young people, with many whose progress has been outstanding on a personal or emotional level feeling like failures following test and exam results," she said.

"With the government's persistent focus on tests, exams results and league tables, many teachers and lecturers also feel under enormous pressure - often at the detriment to high-quality teaching, learning and development of their pupils. Results now appear to be more important than learning, and this does nothing to help children progress."

But a Department for Education spokesman said there is "absolutely no excuse" for teachers cheating.

"Parents will be absolutely outraged to hear anyone admit they've manipulated test scores. It undermines other staff, damages children's education and risks destroying the public's faith in the profession."

He added: "All the leading education systems in the world have robust testing and inspections. Parents and the taxpayer would rightly be asking questions if they couldn't judge how well schools are doing."