Like I say- it is all a moot point because with the NHS tests you don't actually get a certificate that most countries want.
You get a text message or an email with the results, rather than a dated certificate. Plenty of examples of people having issues with this at borders of other countries...
The Government are lying. Plenty of examples this week of people not being able to book tests, being offered test centres hundreds of miles away, people getting to test centres and there being no tests left.