Education watchdog OFSTED has been asked to visit St Peter's Independent School following a complaint which is understood to centre on claims about the alleged handling of a situation involving a small group of pupils, who have since left.

But Gerald Smith, the headmaster of the school, said the claims were "completely unfounded" and insisted they were part of a campaign against his school.

The investigation was instigated after a group of parents made a complaint to Labour MP for Northampton North, Sally Keeble.

She claimed it was important the complaint was dealt with fully and said: "I have therefore asked OFSTED to visit the school to carry out an inspection."

But Mr Smith said he was confident OFSTED would find nothing wrong and said: "These claims are totally unfounded and there's absolutely nothing for anyone at the school to worry about."

After receiving a positive report last time, he said: "I will welcome OFSTED in with welcome arms because that should put an end to all this."

He said: "This is simply a left-wing plot led by a failing Government to try to destroy a successful, low-fee paying, egalitarian, mixed ability, religiously pluralistic independent school.

"The suffering I have been through because of this is beyond belief. But my staff are fully behind me, as are all the governors."

Both OFSTED and the charities commission, which regulates charities such as the school, said they were treating the matter seriously.

Mr Smith has even volunteered to be interviewed by the police over the matter.

In a joint statement the police and the county council said: "We are aware of the concerns raised by parents at St Peter's Independent School.

"An investigation is under way and a member of the staff at the school has been voluntarily interviewed in connection with this matter."

Full details of the complaint have not been confirmed but the statement added: "The investigation is following procedures laid down by the local safeguarding children board Northamptonshire but it should be stressed that the concerns do not relate to incidents of a sexual nature."

The school is due to start its new term on Tuesday.