I too used to work for a scheduled carrier in the UK that did not plan for meal breaks. At the tiem (and maybe now, I'm not sure) the union wasn't recognized by the airline and therefore couldn't do anything about it.
As the sccm, I would rotate the crew at the back and in the middle for boarding duties so that one could be in the rear galley eating with the curtain across the galley entrance. This was far from ideal, but at least they managed to eat. I would just grab something when I could.