Alexander McQueen is not British owned any longer and is currently one of Kering Holland NV brands and, until May this year, Stella McCartney was 50% owned by Kering Holland NV. SM purchased Kering's share back.
I think that if clothes designed by Clare Waight Keller don't pass the 'British' test then neither should those of Sarah Burton of McQueen's as both fashion houses are foreign owned.
I am quite sure that when Harry proposed to her one of the things they knew she would have to give up were any clothes not made in the UK nor made by companies not owned by the UK. Amanda Wakely repurchased her brand back in 2009 and Stella McCartney became the sole brand owner in May this year.
Alexander McQueen is a British brand that’s foreign owned. It was founded by a Brit, it’s headquarters are in London. That’s completely different to Givenchy and Clare Waight Keller.
You can dismiss the DM if you like but The Telegraph, easily the most pro monarchy newspaper in Britain, criticised Meghan for wearing givenchy on the balcony at BP. So clearly their not buying the argument that because CWK is at Givenchy, it all of a sudden makes it ‘British’.