Sent home early without pay or prior notice

[David628]

I work a 30 hours per week contract. For some context, I went through the contract of employment, which states that the hours work on a flexible basis relating to the following clause "The Company reserves the right to increase or decrease your normal hours of work from time to time due to fluctuations in trade" and my time of work would be notified to me by my line manager of my actual work hours that may "vary from day to day or week to week". Recently managers at my work place have been requested to send people home early, an example of such an occurrence would be being sent home at 9, even tho I am on the rota untill 10, and I am not given any notice before this takes place besides "we don't need you anymore, you can go home now". As I am normally being picked up from work by a friend or family member, so this is a massive inconvenience, and it takes me 45 minutes - 1 hour to walk home. So when I come in for only 3 hours it seems rather unreasonable. Is there anything I can do to protest this, or refuse such a early end to a shift? A mate told me I'm required to have reasonable notice, but I'm not sure what I'm legally entitled to.