Q1: Rag, Tag and Bobtail army =? In this context it is suggesting that his !"army" is very second-rate and of poor quality. See here for a discussion of this phrase: Rag, tag and bobtail
Q2: What does 'carbon footprint' refer to? The amount of carbon emissions resulting from your activities. The larger the footprint, the worse for the environment.
Q3: Why does the columnist mention "the West Midlands" here? Because that is where the TUC [Trades Union Council] annual conference is being held - in Birmingham which is in the West Midlands.