A few things as I work in drug testing.
Oral swabs for cocaine will pick up breakdown products from days previous. In other words if you have used cocaine on a Friday night spent all day Saturday in bed and had a night in watching MOD but go to a Sunday game you could very easily still test positive.
The swabs are not confirmatory, like a COVID lateral flow but less accurate, to get a proper confirmation test that meets the judicial standard you would need to send a blood sample to a lab to be tested by a Mass Spec. That is expensive, between 250-350 GBP per sample if we use drug drive testing prices. Let's say you catch 500 people at every Premier league game, 300 GBP a sample that is 150k per game, per Premier league weekend that is 2.7 million a weekend. Are we including FA Cup and League Cup plus internationals?? Cos this already adding up.
So while I think people who use cocaine are a pain in the arse to be around, this sounds like usual hot air shite that no one has the money or properly thought out.