There are checks still to be run on 12 new teachers - and until these have been completed, the school is not opening to all pupils.

Pupils in GCSE and A-level exam years have begun the term as planned.

Head Chris Hassell: "Let down" by the agency

There are also concerns that schools in Leicestershire, due to open on Thursday, may be delayed by the backlog.

Here, 700 checks are still to be done and teachers such as Jane Hanson, may not be able to join pupils as term - which starts earlier in the county than elsewhere in England - begins.

Ms Hanson, who has 30 years' experience, told BBC News the situation was "sad".

"I think it's very sad - it's very sad for the children really, because they're waiting for their new form teacher whom they met last term. I think both cases will both be quite sad that it can't happen."

Huge backlog

The head teacher of Taylor Road Primary School in Leicestershire, Chris Hassell, said the Criminal Records Bureau (CRB) - supposed to be a new one-stop shop for speedy checks on teachers - had let everybody down.

"I do think we've been let down by the agency, because they haven't produced the goods.

The Criminal Records Bureau was meant to be a speedy one-stop shop

"They haven't ensured that people who work with children are checked in sufficient time for them to be employed at school by the start of term."

The Department for Education backed ADT College's decision to keep pupils away, saying that "child protection is paramount and non-negotiable".

The Home Office said later that it was working with the CRB and the DfES to clear the backlog by 4 September, when most schools start back.

It said the CRB would try to make sure "all but a handful" of checks are processed in time.

Head teachers have expressed concern through the summer about the delays in checks on school staff.

Extra staff

The National Association of Head Teachers said on Tuesday that it would be "touch and go" whether checks would be completed by the time the majority of schools return next week.

An extra 100 staff were taken on at the CRB who worked through the bank holiday weekend to clear a backlog of applications.

By Tuesday, 4,000 of the most pressing 25,000 applications had been completed. The entire backlog is estimated at about 100,000.

Eamonn O'Kane, general secretary of the National Association of Schoolmasters Union of Women Teachers, predicted the backlog could still be huge as term gets underway.

This could mean pupils being sent home early as schools struggled to cope with a shortage of staff, he predicted.

Double checks

Following the deaths of Holly Wells and Jessica Chapman, there has been heightened concern about child safety.

Teachers and other adults who work in schools have to undergo a double clearance before they can work with or near children.

Their names must be checked against List 99, the government's confidential dossier of people deemed unsuitable to work with children, including those convicted or suspected of child abuse.

They must also have checks on police records, a process that can take more time as staff may have worked in several different police force areas.

The CRB, a Home Office agency, was set up to provide a speedy "one-stop-shop" to deal with both List 99 and criminal record checks, but delays built up almost as soon as it opened in the spring.