Headteacher Denise Watson noticed a decline in the number of applicants four years ago, but now the quality of candidates has also started to deteriorate.

The school needs 62 teachers for its 1,000 11 to 16-year-old pupils, but some of its vacancies now take up to two years to fill.

Mrs Watson said: “We had to readvertise for a head of mathematics twice last year, and we still need a head of expressive arts which we advertised for twice last year and will again in September.”

She believes that applicants are becoming shrewder and are reluctant to work in schools which could be perceived as challenging. They look harder at education authorities, recent inspection report, and funding levels.

On the other side of the country Bedwellty comprehensive, in Aberbargoed, South Wales, has had to rely on the chair of governor’s daughter - a qualified Welsh language teacher - to step in when things became desperate.

Terry McCarthy, the head, said his school’s “unjustified reputation” has hindered his search for good staff. “The school had been considered to be failing and is in a difficult social area,” he said.

The school needs 28 full-time teachers for its 470 pupils. However, traditional recruitment methods have failed and Mr McCarthy has had to rely on word-of-mouth to fill vacancies this year. Finding Welsh language teachers has been a particular headache.

Mr McCarthy said: “But my chair of governor’s daughter volunteered to do the job as long as I needed her.”