PUPILS' exam results are being threatened by a national shortage of teachers, council leaders have warned.

The claim was made by a group of seven local authorities across the North of Scotland facing acute difficulties in recruiting staff - particularly in so-called Stem subjects such as science and mathematics.

Councils and teaching unions also warned current problems are being exacerbated by a ministerial policy to protect teacher numbers.

Under the initiative, local authorities are required to maintain their existing numbers even if pupil rolls shrink. Critics argue that means some councils have too many teachers at the same time as others are struggling to recruit.

A joint statement from the Northern Alliance, which include Aberdeen, Aberdeenshire, the Highlands and Moray, said: "There are serious concerns in relation to recruiting certain subject specialisms in secondary schools, particularly in the Stem subjects, home economics and modern languages and there are serious risks to attainment in national examinations as a result of this."

In March, a major report on the state of the nation's schools by inspectors from Education Scotland also concluded classroom standards were facing an impact from shortages.

On the issue of national teacher numbers, the Northern Alliance said: "It could be argued the agreement has done nothing to help as some local authorities report an excess of teachers, whilst not being able to release them in order to maintain their ratio."

Cosla, the umbrella organisation for councils, backed the concerns stating: "The continued focus of government on teacher numbers as a key performance indicator of councils’ commitment to maintaining and improving education outcomes is unhelpful.

"It skews the issue of recruitment to fulfil a national staffing ratio rather than allow councils to seek to recruit the most appropriate numbers of teaching staff to meet the needs of children and young people in their schools."

The Educational Institute of Scotland (EIS) teaching union, which has always backed the policy on protecting teacher numbers, also called for change with the introduction of a national minimum staffing standard.

The union said: "Whilst the arrangement gives certainty about the overall level of teacher involvement in education in Scotland it has proven to be restrictive for local management and efficient deployment of resources.

"It can also mask a wide variety of staffing models across Scotland... and it can preclude any significant local adjustment when there are changes in pupil numbers within the school year. An alternative... is to develop and agree a minimum staffing standard."

A Government spokesman said: "We are investing £88 million this year alone so every school has access to the right number of teachers, with an additional £3m to train an extra 371 teachers in 2017/18.

"We are committed to maintaining teacher numbers nationally. Our deal with local authorities to maintain the pupil teacher ratio has halted a period of steady decline in teacher recruitment by councils and resulted in 253 more teachers last year – the first substantial increase since 2007.”

The Northern Alliance also said additional money for schools to tackle the impact of deprivation had led to extra teachers being recruited in urban areas exacerbating shortages elsewhere.

Universities which training teachers have previously called for a move from one year to three year planning on teacher numbers to improve current shortages.

The full extent of the problem was revealed last year when it emerged there were 730 unfilled vacancies across 27 of Scotland’s 32 council areas.