I did web search about it and it says that when split, they can expand when they get wet, making them harder to swallow. This makes me wonder if it's all about a choking risk. A time-delay for effectiveness doesn't make sense.
I wonder if the UK pills are different or if they just have a different risk tolerance?
Perhaps you might try the powder form of Renvela and just use half or a quarter of the contents (depending on the food's phosphorus load.It has a bit of a lemon flavor, so you might want to mix it with tea.