Nearly three-quarters of Barnet's schools were due to close or partially close today because of teachers striking over below-inflation pay increases.

Seventy-five of the borough's 106 state schools are affected by the National Union of Teachers (NUT) strike, with 30 being forced to cancel all lessons.

The first national teachers' strike for 21 years will hit an estimated 3,346 schools across the country.

Friern Barnet School, in Hemington Avenue, is one of the 45 schools to partially close after a third of its staff decided to stay away.

Headteacher Jeremy Turner said health and safety considerations forced him to cancel classes for Years 7 to 10, but he said he was not opposed to the strike.

He said: "Teaching is a profession and we want teachers to be paid a professional rate. It all comes down to whether you believe strike action is an effective method for enacting change or not.

"As headteacher, I need to balance the right of my colleagues to strike and the right of students to learn."

Tim Harrison, NUT secretary for London, said the strike was more important for Barnet than other areas of the country because the borough needed to attract teachers away from central London.

He said: "It is a national campaign but the impact of declining salaries is always greater in outer London than elsewhere.

"Barnet is as expensive a place to live in as central London, but less attractive to youngsters straight out of university. Only five years ago we had a severe teacher shortage here."

The strike is in response to a pay increase of 2.45 per cent rise this year, with a further rise of 2.3 per cent in 2009 and 2010. The NUT wants pay rises equivalent to the rate of inflation, which is currently 4.1 per cent under the retail price index (RPI).

Three-quarters of NUT members voted in favour of industrial action, on a 32 per cent turnout. This represents about a tenth of teachers in England and Wales.

The day off will be welcomed by many students, but not all were happy with the closures.

Year 9 pupil Harry Ford, from Mount Grace School, in Church Road, Potters Bar, said: "I want my education to stay focused and, if we end up not coming into school, it's us students who will be affected."

Hendon's Labour MP, Andrew Dismore, said: "The NUT should be negotiating, not striking.

"They are clearly doing it in the period before an election to blackmail the Government into giving them what they want. The Government needs to keep inflation under control and cannot spend money it doesn't have."

Labour MP for Finchley and Golders Green, Rudi Vis, said he did not object to the strike.

He added: "This is about pay and conditions. The Government has done a great deal but it has not done enough. It is time we paid particular attention to these people and the service they provide."

Lecturers and academic managers in the University and College Lecturers Union (UCU) will be forming picket lines at Barnet College sites in Wood Street, High Barnet; North London Business Park, Oakleigh Road South; and Grahame Park Way, Hendon, in an attempt to bridge the pay gap with schoolteachers. Lecturers' average pay is around six per cent less than equivalent teachers.