They can tell you to wear suspenders and a bra, but would you? (actually, don’t answer that)
It’s down to you mate. You’re the one carrying all the responsibility of driving a heavy goods vehicle. If you crash and burn a family because you were driving tired, who takes the blame? Your office, or you? Try telling the judge your office “told you to take a break when they wanted you to have one”. The office would deny it, and the judge would throw the book at you.
Tell your office, politely, that you’ll take a break when you feel the need, then do it. You’re the driver. You’re the captain of your ship.