Hi, I have recently started doing deliveries for a company on a pushbike, I have completed all my training and had started doing deliveries for 1 week when I then received a call from a pre-employment agency telling me that I need to come in for a physical, it was then booked, I still at this point had not been told by my boss that I would have to go for one. 3 days before i was due in for the pre-employment examination I was told that it would include a drug test by the agency. I want to know if I have any legal grounds here to refuse the pre employment drug test, as I thought employers had to give warning of doing so, also because I had already began work then they told me that I had to do a pre employment check.