But he has been forced to skip the chance to exchange ideas with colleagues in Birmingham this weekend. The London-based head will not be attending as his school, Christ’s College in Finchley, simply cannot afford to send him.

It needed pound;4 million this year just to achieve a standstill budget even before the extra costs of implementing the teacher workload agreement were considered.

Now, Christ’s College has found itself with a pound;450,000 shortfall. “I have never known it as bad as this and this is supposed to be a year when we have got a good funding settlement,” said Mr O’Shea. “The Government is in denial saying that there is nothing wrong with the funding formula.

There must be something wrong.”

The school is already looking for volunteers for redundancy among support staff and teachers. Mr O’Shea aims to avoid compulsory redundancies but worries this will store up the “pain” for future years. He has been “pulling his hair out” trying to work out how he can manage and expects cuts in training, textbooks and materials and building maintenance.

And what of the teacher workload agreement? “At the moment we consider that to be a bit of a joke,” he said.