Schools must allow parents to shop around for uniforms at Asda and Tesco, the Competition and Markets Authority has told the Government.

In a letter to the Education Secretary, the chair of the CMA said they receive a “surge of complaints” from parents and carers every summer about the “excessive cost of uniforms where school policies prevent items being purchased from cheaper alternative suppliers”.

Often schools insist on parents purchasing uniform from a particular supplier, despite much cheaper – and often identical - alternatives being available in supermarkets.

Lord Andrew Tyrie urged Gavin Williamson to introduce statutory guidance for schools on the issue, warning that “action is needed as soon as parliamentary time allows”.

He explained that in 2015, the CMA wrote to schools and school uniform suppliers, reminding them that competition law may prohibit certain conduct and exclusive arrangements between schools and uniform suppliers.

“Having considered this issue many times, the CMA has concluded that statutory guidance is needed as the simplest and most direct way of delivering change,” he added.

On Wednesday, the schools minister Lord Agnew vowed to crackdown on schools using “monopoly suppliers” for their school uniform.

hen questioned over the cost of school uniform during a select committee hearing, he said: “There is a specific problem of a relatively small number of schools who use this requirement of monopoly suppliers for school uniforms and I don’t like it because it’s a pernicious way of excluding children from less well-off backgrounds.”