In house Breathyliser and drugs testing

ive only had 1 instance when i was unfortunate to work for a while agency in tesco.
if your a day man and back to base all the time,then theres no biggy if your already working for a plobber company like that.
i took a guys front bumper off,did the delivery,back to the yard for a debrief and murder inquiry and did the breath and pee test with a doctor they bring in.
no biggy.
having lost all self respect by demeaning myself to work there in the first place,then its easier to just do whatever they want to varying degrees ( this includes leaving your brain and any aspect of rational thinking to get the job done in your car in the carpark at the start of your shift).
ive never worked ,nor would i work for any company that did breath tests though to be fair,most of the ones i would work for would be hooligans anyway.
if your a tramper,then theres not much point unless your the sort who turns up monday morning smelling like a distillery,or your shift partner has dobbed you in for the empty cans of special brew lying in the cab.

legally,dont they need to give you notice of any contract changes and then you decide to bend over or leave?