The couple initially delighted parents at their youngest son Leo's school by offering to host the party at their seven-bedroom mansion near Chequers.
But the mood of some parents darkened when they discovered that the Blairs were charging each person £10 for a seat on a coach from the school in Central London to the mansion in Buckinghamshire. According to one London coach hire company, the cost would be between £375 and £500 depending on the size of the vehicle required.
The Blairs have banned parents from driving directly to the estate for security reasons, asking parents to board the bus instead.
One mother of a child who is in Leo's year said: 'I'm livid. The Blairs are rich and can afford it, but lots of families in the area are poor.'
Kevin Norbury, a dustman whose children attended the school, said: 'I think he's tight charging these people, given the amount of money he's got.'
Another parent added: 'If the Blairs are holding the party, it's up to them to make the transport arrangements. I've taken a group of pupils, parents and teachers on a day out and hired a minibus, and didn't charge anyone anything.'
A spokesman for the Blairs said: 'The Blairs have agreed with the headmaster that if any family can't afford the cost of the coach, then they won't have to pay.'
Since a potential kidnapping plot in 2006, the Blairs have been keen to protect Leo's privacy and have decided to keep the identity of their youngest son's secondary school a secret.
Cheeky to charge, or OK? Tell us your thoughts.