Katharine Birbalsingh (pictured) is imposing the 'lunch isolation' on pupils to encourage parents to 'change their ways' and support their children

A headteacher who made her name at a Tory party conference by claiming Britain's education was 'broken' is forcing children to eat by themselves and restricting food as a punishment for their parents failing to pay for school lunches.

Katharine Birbalsingh, a favourite of former education secretary Michael Gove, is imposing 'lunch isolation' on pupils whose parents are behind on payments.

Children who are put in lunch isolation are given a sandwich and piece of fruit instead of their usual hot meal with dessert, and made to sit on their own for the whole lunch hour.

Critics called the measure at Michaela community school, a secondary free school in Wembley, north London, 'stigmatising'.

But Miss Birbalsingh said it was an attempt to encourage parents to 'change their ways' and support their children.

She rose to national prominence when her speech at the 2010 Tory party conference about failing schools provided the backdrop to Mr Gove's sweeping education reforms.

The sanction emerged in a letter from deputy head Barry Smith to Dionne Kelly, who fell behind on meal payments for her 12-year-old son Reon. It read: 'The deadline for this term's lunch payments was 1st June 2016. 'You are currently £75 overdue. If this full amount is not received within this week your child will be placed into Lunch Isolation.

'They will receive a sandwich and piece of fruit only. Only when the entire outstanding sum is paid in full will they be allowed into family lunch with their classmates.'

Ms Kelly, an unemployed care worker, said she had already paid the money by the time the letter arrived, but Reon had received the punishment anyway.

She said: 'I found the letter quite threatening. Isolating children for their parents not paying upfront is degrading. It's embarrassing for poor families.' The letter appeared to be addressed to several parents, as it began with the address: 'Dear families', but the school would not say if others had received it.

Ms Kelly, a single mother, received the letter only two weeks after Reon had started at the school. She said she had not yet registered for free school meals, but planned to try to claim the money back.

The school charges meals at £2.50 a day, with payment required upfront. She has now moved Reon to another school.

The school has a traditionalist academic ethos with a long school day: 7.55am-4pm. Full lunch menus at Michaela, which markets itself as having a 'private school ethos' but with 'no fees', include meals such as vegetable bolognaise pasta bake and salad followed by chocolate crunch, or vegetable tikka masala in a jacket potato with iced sponge for dessert.

The sanction emerged in a letter from deputy head Barry Smith. Children who are put in lunch isolation are given a sandwich and piece of fruit instead of their usual hot meal with dessert, and made to sit on their own for the whole lunch hour

Critics called the measure at Michaela community school, a secondary free school (pictured), 'stigmatising'

Miss Birbalsingh admitted that she and Miss Kelly 'did not see eye to eye', and insisted Miss Kelly had not paid for her son's lunches. Miss Birbalsingh added: 'The letter from Barry Smith…was sent in an attempt to encourage mum to change her ways and support her son by paying for his food.

'The vast majority of secondary schools use isolation to discipline children.'

Miss Birbalsingh added that the lunch isolation was part of half a day in isolation imposed because of poor behaviour the day before.

Sam Royston of the Children's Society, said: 'No school should punish and potentially stigmatise a child because a parent has not paid for, or is unable to afford, school meals.

'Schools should be doing everything they can to support parents who may be struggling with the costs of feeding their children.'