Extensive clinical evaluation from Public Health England and the University of Oxford show Lateral Flow Tests are accurate and sensitive enough to be used in the community, including for asymptomatic people.
From NHS England’s FAQ on the lateral flow antigen tests
“Q17. Will this testing regime remove the need for staff who have been exposed to a positive Covid-19 case to self-isolate?
No. Government self-solation advice should be followed at all times. This test does not remove the need to self-isolate.”
Point the above out to your friend Clark so he can point it out to his employers.