Norfolk headteachers whose pupils have returned lower English GCSE results than expected have spoken of how 'the goalposts were moved'.

Concerned teachers across the country have suggested that GCSE English exams were marked too harshly this year after schools reported an unprecedented number of fails among their pupils.

English teachers who were shown early breakdowns of the marks have complained that exam boards had substantially increased grade boundaries, leaving pupils with lower results than expected.

It comes amid predictions that the pass rate across all subjects will start to stall.

Stuart Bailey, headteacher of Swaffham Hamond's High School said English GCSE results were 5pc below predictions.

He said: 'There are fewer kids here getting their grade than we thought. We have seen their work and we have graded it at a certain standard and we know what they should be getting and, all of a sudden, the goalposts were moved and that does not seem fair, but we have still made improvements.'

Ian Clayton, principal at Thorpe St Andrew High School in Norwich, said: 'It all seems a little unclear at the moment. Our grades for English are slightly down on what we expected and that's had a slight impact on our headline rate [five or more A* to C grades, including English and maths].

'We're focusing on those students who needed a C for sixth form or college places but didn't get it – that's the important bit. We're looking to see if they need to be remarked.'

The Association of School and College Leaders (ASCL) said there seemed to be a particular problem with C/D borderline grades in English, with pupils who were expecting Cs ending up with Ds.

ASCL general secretary Brian Lightman said there was 'a lot of concern' among members about the changes to grade boundaries.

'We expected results to plateau because of the Government taking steps to peg them to previous levels,' said Mr Lightman.

'But we certainly didn't expect anything like this and schools have been taken by surprise.

'We've got some schools where teachers have been teaching the same course for years and suddenly the results are way below what they've always been before as the pass mark has been moved higher.'

Dozens of teachers voiced their concerns about the issue on the Times Educational Supplement's website last night.

One said that the score out of 80 needed to get a C grade was now a whole 10 marks higher than earlier in the year. He added: 'They've not moved the goal posts, they've put them on a different chuffing planet.'

Another said: 'Our results have been decimated. We're 10% lower than last year.

'Members of my department are in a state of shock as they say they've never worked harder and this is the result.'

An ASCL spokeswoman blamed the Government's 'constant tinkering' with the exams system, adding: 'They are fiddling and manipulating them all the time which is not fair for the kids who have worked really hard and have been working at a C grade level but now may not have got one after all.'

Last year 69.8% of GCSE entries gained at least a C grade, and 23.2% got an A or A* but one expert predicted the pass rate will stall this year.

Professor Alan Smithers, of the Centre for Education and Employment Research at Buckingham University, said schools put a lot of effort into making sure pupils score at least five C grades, including in English and maths, as they are judged on these results.

But Ofqual has told exam boards they will be asked to justify any results that are widely different to previous years in a bid to tackle grade inflation and ensure results are comparable.