The National Union of Teachers has said it will be appealing a decision handed down by a High Court judge that it “unlawfully interfered” with Timeplan’s recruitment advertising. The case, which will push up the NUT’s legal bill (already in six figures), is expected to take months to come to court.

Steve Sinnott, NUT deputy general secretary, said: “It has cost a lot of money. But we regard this issue as one that is very serious indeed. What we are beginning to see is the gradual erosion of nationally determined pay and conditions for all teachers.”

Timeplan, which has been operating for six years since the demise of the Inner London Education Authority, has an annual turnover of Pounds 10 million and 2,500 teachers on its payroll. Many of its supply teachers are from New Zealand and Australia.

The case began with the agency issuing a writ against the NUT after the union wrote to the magazine of its sister teaching union in New Zealand asking it to stop carrying advertisements for the company. The magazine ceased to run the ads and Timeplan lost business.

The NUT is concerned that Timeplan pays a flat daily rate of Pounds 80 to its supply teachers and that it was using supply teachers to cover long-term and even permanent vacancies. Tish Seabourne, Timeplan’s managing director, who used to work for the ILEA, said 85 per cent of Timeplan’s teachers were paid more than national pay scales and that average placements were 3.5 days.

When the judgment came down in June, the union was ordered to pay damages to Timeplan expected to amount to a six-figure sum. The Department for Education and Employment is to issue guidelines on use of agencies by Christmas.