Sussex children return to school next week for the start of the new school year - but thousands could be turned away on the first day back.

When the school bells ring, it is likely to be teachers who are marked absent.

Hundreds of teachers and classroom assistants may be unable to take up their new posts because child protection checks on their backgrounds have not been completed.

Without official clearance, they cannot enter a classroom and thousands of children face being turned away.

With just four days to go before schools go back, the system is in chaos.

Schools are unsure how many teachers will be able to report for duty or how long it will be before they are cleared to start work. It is making planning extremely difficult. Teachers, education chiefs and union leaders are fuming.

The Criminal Records Bureau (CRB), which is handling the vetting procedures, has taken on extra staff in an 11th hour effort to clear the backlog.

But education chiefs must wait until Monday or Tuesday to see how badly schools will be hit.

East Sussex County Council put in more than 1,000 requests for clearance. They are still waiting for approval on 400 staff, half of them teachers.

A spokesman for the council said: "It is possible children will have to be sent home."

The education authority is hopping mad about the delays, which it forecast months ago.

Matt Dunkley, assistant director of education, said 90 East Sussex schools were involved.

"We are extremely annoyed about the fact we predicted we would be in exactly this situation as long ago as April and May.

"We are annoyed we have not been able to use our old tracking system. If they had gone for a twin-track approach and allowed us to continue our own checks in tandem with the new system, this may not have arisen.

"In principle I support a single central check - it is a sensible idea. But the way it has been run is a disaster."

While the CRB ploughs through the backlog, local authorities have instigated contingency plans.

The Department for Education and Skills (DfES) has said written evidence from a previous employer that a teacher has been police- checked in the last three years is acceptable while they wait for the full CRB check.

Mr Dunkley has been forced to call in 20 staff to work today to try to carry out checks with people's previous employers.

The authority will also hold a last-minute crisis meeting with school representatives on Tuesday.

But, until headteachers know exactly how many staff are affected, they cannot finalise plans.

A spokesman for East Sussex advised parents to watch for the latest media reports and, if worried, contact their children's school before term starts.

In West Sussex schools are bracing themselves for disruption, with 714 checks outstanding.

A spokeswoman said: "We are in a position of not really knowing exactly what the difficulties will be until Tuesday and our schools start back on Thursday. We could have disruption.

"However, as far as the authority is concerned, safety is paramount and we are sure parents will understand we don't want anybody to teach or help in the classroom unless they have gone through the process and been cleared.

"The checks are imperative and it is very important we receive the certificates in good time for people to take up their new positions."

She said the DfES had notified them that all checks would be completed by the start of term.

However, as a precaution, the authority has faxed and emailed all its schools telling them, providing an employee is joining from another authority and there has been no break in employment, they can use references as a stop-gap.

However, if a teacher or assistant is joining after a break in service, is a returner, comes from a private school or abroad or is recently qualified and does not have a certificate, they cannot work with children.

The situation appears less acute in Brighton and Hove.

Checks are still awaited on 195 staff. Of those, 51 are classed as priority cases and the council has asked the CRB to fast-track them through the system.

A spokesman said: "We are confident the priority cases will be cleared and we are hopeful the others, which include admin people, mid-day supervisors, caretakers and learning support staff, will too."

Paul Munbt, national executive member of the NAS/UWT for Sussex, called the situation "an appalling state of affairs".

He said: "We should ensure our children have the very best start for the school year - that's what kids deserve and parents expect. It is also very unsettling for new members of staff.

"We have known about this for some time, so have the local authorities, but the Government has chosen to ignore the danger signs."

He said the problems had been caused on two fronts - the Government's decision to privatise vetting procedures and its failure to get to grips with teacher's workloads and salaries and attract the right calibre of people into the profession.

Mr Munbt said although it was possible children could be turned away, it was likely schools would cope using supply teachers.

The DfES has insisted thorough vetting is "paramount and non-negotiable".

Vetting is not new but the system has been tightened up. Under the old system employers carried out what was known as a List 99 check with the DfES to see whether a potential employee was on the official blacklist of people unsuitable to work with children. The police also checked criminal records.

In March this year, the CRB took over responsibility as the "one-stop shop" for checks. However, it quickly became apparent it could not cope.

In May, the DfES told employers to adopt an interim arrangement, in effect the old system but done through the CRB. The DfES said as long as a List 99 check had been completed, schools could appoint teachers and other classroom staff provisionally, pending completion of a full police check.

However, following the tragic deaths of ten-year-olds Jessica Chapman and Holly Wells, the DfES insisted everyone, including ancillary staff like caretakers, contractors or school governors, must obtain a full disclosure from the CRB.

Some checks on Sussex teachers could be carried out in India. Capita, the company running the contract for the CRB, has set up a call centre in Madras.

Thousands of application forms have been scanned in Britain and emailed to India for processing.