Britain's biggest police force faced a staffing crisis today after 95 per cent of its 999 call handlers failed to turn up for work because of the national strike.

The number - which relates to 192 out of 202 members of police staff - was revealed by Scotland Yard commissioner Sir Paul Stephenson, who warned that the public were receiving a "degraded" service because of the walk-out.

Sir Paul said that 335 officers had to be taken off their usual beat to man the phones.

But he warned that, due to officers not being used to handling the sophisticated call-handling and despatch technology, calls were being handled slower than usual.

Speaking to members of the Metropolitan Police Authority, he said: "90 per cent of police staff call handlers have not turned up for duty. It is a very, very significant number.

"While I fully understand the lawful right of people to withdraw their labour in certain circumstances...I am the commissioner of the Met and my job is to run a police service.

"This problem means there are less officers available on boroughs and it is blindingly obvious that the service we are giving is necessarily degraded.

"I think we are doing a good job, but the reality is that the amount of time we are taking to answer calls has increased.

"I am concerned, and you would expect me to be concerned, by this level of no show in an emergency service."

The target for answering a 999 call is 10 seconds - but currently it is taking an average of 15 seconds to answer calls.

It comes as hundreds of thousands of public sector workers have begun to strike across the country, closing or disrupting schools, colleges, courts, Government offices and job centres.

Port and airports are being affected, causing travel chaos for holidaymakers trying to head abroad. Anyone arriving in the UK today is likely to be among those facing long queues.

The impact of the strike began to be felt as early as last night as border control staff refused to turn up for work.

Early indications this morning were that the estimate of 750,000 strikers could prove to be accurate and some union officials said they expected "the best supported strike we have ever seen".

The Government believes public sector pensions need to be altered because the cost to the taxpayer is too high as life spans increase.

However, unions believe the "devastating" changes to be unjustified and claim they will lead to poverty after retirement for too many people.

Those on the 24-hour walkout are the National Union of Teachers, Association of Teachers and Lecturers, University and College Union and Public and Commercial Services union.

The strikes are set to affect:

Schools: At least 7,800 schools, nurseries and education centres in 143 areas in England alone are expected to be affected, although the numbers are likely to be higher. The NUT has estimated that around 85% of schools will be hit, which equates to around 17,000 schools in England.

Colleges: The UCU said 350 colleges and 75 universities in England face "significant disruption" as lecturers join the stoppage.

Job centres: The PCS said jobcentres across the UK will close or only offer limited services, while people ringing call centres for advice could be met by recorded messages.

Driving tests: The Driving Standards Agency urged all driving test candidates booked to take a test today to attend as usual, saying they will be given a new date if there is a cancellation because of the strike.

Courts: Thousands of courts staff as well as those who transport prisoners are involved in the action, threatening cancellation of cases or delays to trials.

Ports and airports: Immigration and customs staff will strike, leading to the prospect of lengthy queues and delays for travellers.

Prisons: Members of the Prison Officers Association will stage protest meetings in a show of support to the teachers and civil servants.

Coastguards: Maritime and Coastguard Agency staff belong to the PCS union but it is not clear how widespread any disruption will be.

Houses of Parliament: Security staff will be on strike and picket lines will be mounted outside, possibly leading to some left-wing MPs refusing to cross them.

Tax and customs: Offices across the country are set to be hit by walkouts, which the PCS said will disrupt tax processing and other services.

Rallies and marches are being held across the country, including Aberystwyth, Birmingham, Bradford, Bristol, Cardiff, Colchester, Derby, Dover, Exeter, Glasgow, Hull, Leeds, Leicester, Liverpool, London, Luton, Manchester, Newcastle upon Tyne, Norwich, Nottingham, Oxford, Plymouth, Portsmouth, Reading, Sheffield, Southampton, Swansea, Wigan, Wrexham and York.

Leaders of the four unions involved in the strike will attend a march and rally in central London, which is expected to be attended by thousands of union activists.

Students, anti tax avoidance group UK Uncut and other campaigners will also stage demonstrations in the biggest outbreak of industrial unrest since the coalition Government was formed over a year ago.

Official calculations yesterday showed that a typical teacher can expect to retire with a taxpayer-funded scheme worth more than £500,000.

Treasury figures released today expose how public sector retirement funds dwarf their private sector counterparts.

The calculations show that a mid-ranking teacher on £32,000 a year will receive a final salary pension that is the equivalent of having built up a £500,000 pension pot.

This is 20 times higher than the average private sector scheme, according to figures from the Office for National Statistics. Private sector workers would have to save more than 20 per cent of their salaries for 40 years - more than £500 a month for a similarly paid person - to amass the same amount in a defined contribution pension.

A well-paid London headmaster will retire with a pension scheme worth £1.5million, the Treasury figures show. A chief constable retiring at the standard age of 55 would have a scheme worth more than £3m.

Every British family faces a total bill of £13,500 to pay pensions for teachers - up to 300,000 of whom are expected to join the strike. David Cameron has said the disparity between the public and private sectors is "unfair".

The Government hopes that the figures will prove that the strikes are unnecessary.

A government source said: "We believe that if the situation regarding pensions is explained to people, the rationale for strike action disappears. Reform is essential."

Last night, business leaders attacked the "apartheid" between public and private sector pension schemes and urged unions to call off their strikes.

Miles Templeman, the director-general of the Institute of Directors, said: "Immediate public sector pension reform is absolutely necessary if Britain is to have sustainable public finances in both the short and long run. This is not a race to the bottom, as public sector unions claim - it is a race to reality."

The figures were released after unions warned that 4m public sector workers were planning to strike this autumn unless the Government backed down.

The Prime Minister urged employers to let people "take their children to work" to face down the trade unions who are threatening to undermine the economy.

Fears mounted that the protests, including picket lines across Whitehall, could be hijacked by anarchists. Police leave has been cancelled as an expected 10,000 striking workers march through London.

At a Westminster meeting yesterday, the head of the civil servants' union warned of "apocalypse" in the autumn with millions of public sector workers walking out.

Mark Serwotka, the general secretary of the Public and Commercial Services Union, said 750,000 workers would be on strike today.

But he warned the Government: "If you won't talk to us we will ensure the next national strike has three to four million of us."

The industrial action is expected to cost the economy more than £600m as hundreds of thousands of parents take time off work to care for their children at home.

A survey by The Daily Telegraph of local education authorities in England found 45 per cent of schools under their control would be at least partially closed for the day.

Almost 30 per cent of schools will be shut but in some areas nine out of 10 state schools will suffer major disruption.

The Department for Education said the latest figures showed that more than 5,400 schools in England would be fully or partly closed - about 25 per cent.

Mr Cameron told MPs yesterday that the strikes were not justified, as negotiations over the pension reforms were still continuing.

He said: "What we are proposing is fair - it is fair to taxpayers but it is also fair to the public sector."