Free school meals

https://www.gov.uk/apply-free-school-meals

Rules vary by country, here they are in England:

Income Support
income-based Jobseeker’s Allowance
income-related Employment and Support Allowance
support under Part VI of the Immigration and Asylum Act 1999
the guaranteed element of Pension Credit
Child Tax Credit (provided you’re not also entitled to Working Tax Credit and have an annual gross income of no more than £16,190)
Working Tax Credit run-on - paid for 4 weeks after you stop qualifying for Working Tax Credit
Universal Credit - if you apply on or after 1 April 2018 your household income must be less than £7,400 a year (after tax and not including any benefits you get)

Relevant legislation: Education Act 1996 https://www.legislation.gov.uk/ukpga/1996/56/section/512ZB

politics.co.uk says this, though I didn't see a source:

As of January 2020, 1.4 million pupils – about one-in-six – were eligible for means-tested free meals, bringing the total yearly cost to around £600 million.

And bigissue.com says, also without a source AFAICT:

Westminster pays a flat rate of £2.30 for every child per meal in England who claims free school meals. This figure which has not risen in several years despite inflating food costs. It costs the government around £20 million a week.
The cost varies between councils in Scotland, averaging at £2.15 each and most expensive in Aberdeenshire at £2.50. Meanwhile in Northern Ireland, school meals cost £2.70 each.

No files, tests, or entry points are named. Start by reviewing the linked GOV.UK guidance and Education Act 1996 section 512ZB, then locate the relevant UK policy modules and tests; done should mean the England free-school-meals rules and any supported amounts are represented and covered by tests.