I often get enquiries about redundancy pools and who should be included. The answer is there are no rules that specify who should be included or who should not. These are business decisions and employment law generally leaves business free to make those decisions.
The key is to make a reasoned decision about the pool for redundancy that you an demonstrate you applied your mind to. That usually means that when you make the decision you make a note of the factors you considered and the decision you came to. As long as that decision satisfies the range of reasonable responses test, i.e. was your decision one of a range a reasonable employer might come to, that will be enough. Quite a low threshold really.