Funnily enough I stayed at the Hatton Cross HGI last night and someone asked me a similar question. It's possible to walk from there to T4 relatively easily, following the roads by The Duke of Northumberland Canal, not quite a bucolic experience, but it could be worse. From T4 to T5 is also walkable, and I have done that myself. T2/3 is undergoing tunnel work and even cyclists are temporarily banned from cycling to these terminals. So at least for the time being some alternative is needed to get to T2/3