Ministers said they refused to believe that teachers would not want to apply when they stood to get a rise of �2,000

Almost 80% of those who were eligible did apply - but that did not stop them objecting to the new system.

One of the main complaints is that it is divisive. They say teaching is about teamwork, and it is wrong to single out some members of the team for special treatment - especially in small schools.

An aspect of this is that it is almost impossible, they say, to identify which teacher or teachers might have contributed to a child's progress.

Another concern, pursued most forcefully by the National Union of Teachers, relates to the way assessments have to be carried out.

New conditions

As part of this process the government amended the teachers' conditions of service to require teachers to assist head teachers in assessing those who were applying to go through the threshold.

The government said this meant simply that heads of department would be consulted.

The NUT said it would turn all teachers into "informers", leading to a culture of snooping, distrust and favouritism in schools.

It successfully applied for a judicial review over the government's handling of the regulations, arguing that there had not been the required period of consultation.

The review was heard at the High Court in London and on 14 July Mr Justice Jackson ruled that the government's amendment to teachers' conditions was illegal.

The government then consulted on the changes, through the School Teachers Review Body which advises on pay and conditions.

This recommended that revised wording was needed to make it clear that only teachers' line managers would have to assist head teachers in assessing their applications. The government accepted this.

Two-tier system

Although the unions have often been vociferous in what they have had to say about performance pay, they have worked with officials to refine the system.

Even the NUT is providing advice to its members if they wish to apply - exposing itself to charges of hypocrisy, but arguing that it does not want to disadvantage individual members.

One change it won during the consultation was that there should be a right of appeal for teachers whose applications were turned down.

And there is pressure on teachers to apply: even before the structure is fully in place some schools were advertising for teachers "good enough" to cross the threshold.

They say they want only the best candidates for jobs and would be suspicious of applicants who were on the top of the old pay scale but had not chosen to try to move onto the higher scale.