I work in hospitality in a pub chain in the UK, where I regularly work long shifts without getting a break. The shifts I am on mean that I am often on my own in the pub's kitchen for a large majority of my shift (I work as a cook.) This means that is unreasonable that I'll be able to get a break; there is simply far too much work to do- for example, if it is busy, I cannot just go for my break otherwise there will be nobody cooking. Even on shifts where I am not on my own, if it is busy there is a good chance that I will not be taking a break.
Today I had an argument with my boss. She is saying that I should just walk out of the kitchen and go for my break. In the past this has never been communicated to me. As well, it is to my own jeopardy, since if I do go for my break, I will be blamed for not getting adequate amounts of prep done. Since there is nobody covering me, I am unable to take my break, even if my boss says otherwise; in the past I have done shifts upwards of 8 hours with no break. She went as far as saying I should just eat before my shift in anticipation of not getting an interrupted break, despite the fact that I start at 6am, which seems like an unreasonable request (as is right now I am going the entire day without eating due to not getting a break.)
My boss is now telling me that because I take cigarette breaks, this counts as a rest break. Whilst I do deduct the time it takes me to smoke from my overall break entitlement, I fail to see how it is at all comparable to the food break outlined in our company policy. For context, I will take 2-3 5 minute cigarette breaks, when my overall break entitlement is 30-45 minutes (depending on my shift.)
TLDR; my job makes it impossible to take breaks, and my boss is expecting me to leave an entire kitchen unattended whilst I go for my break. Is this illegal, even if I do take my cigarette breaks?
Any and all advice is appreciated, since I would really like to make a formal grievance.