Can i be sacked if a refuse to do more than 9 hours work with more jobs being put on to me to do?

i do multidrop sometimes get 30 maybe more jobs , and each jobs takes time and parking is difficult sometimes i shouldnt work through my lunch break which is against the law but i do to get much done as poss but my employer is wanting more work after sacking 13 drivers which we are under pressure and threaten to be sacked i do have alife after work which im not getting a the mo