The Royal Mail sorting office, which is handling applications dealt with by headteachers, has this week been swamped with letters. The huge postbags have prompted a complaint from postal workers to the company vetting applications on behalf of the Government.
Unofficial polls by the teacher unions shows that the vast majority of the 250,000 teachers eligible to apply - at least 80 per cent - have done so.
And Nigel de Gruchy, general secretary of the National Association of Schoolmasters Union of Women Teachers, said: "It could be up to 90 per cent, although there are a few pockets of opposition."
In England the closing date for applications to cross the threshold, putting teachers on a PRP scale where they could earn up to pound;30,000, was June 5. The deadline for Welsh teachers is September 29.
Cambridge Education Associates, the company vetting the forms, said official figures would be available at the end of this month.
All staff at the Cambridge-based firm have been sworn to secrecy but the town's postal workers have reported huge postbags being delvered to the company.
But many of the letters were posted unstamped and one postal-worker, on being told by The TES that the letters were from teachers seeking a pay rise, said:
"They're hardly likely to get it, if they don't even stamp the letters."
While many heads were determined that staff hit the deadline, others have been more lax, saying applications did not have to be submitted until July 31 - the date on which applications are supposed to be passed on to CEA.
Hackney Council, in east London, said at least two teachers at Kingsmead primary would receive training on applying for the threshold next week - more than two weeks after the official deadline.
The move follows claims that they were initially denied information. One of the teachers claimed the majority of staff, opposed to PRP, made the decision not to hold a training day in his absence.
National Union of Teachers members in Hackney said the majority of the borough's teachers had refused to apply.
Heads were this week receiving more training to help them assess applications, amid complaints that the sessions were too short and gave messages which conflicted with earlier training. A Department for Education and Employment spokesperson said 91 per cent of heads were satisfied with the course.