Interesting figures above. There are some details that caught my attention, e.g. that Dusseldorf is such a strong destination from BHX (and als MAN) compared to other German airports including the two much larger airports of MUC and FRA. And what also strikes me is the extreme seasonality of Palma as a destination from the UK. You have dozens of daily flights to Palma from German airports in winter, so holiday patterns obvioulsy are very different (from the UK mostly beach goers, from Germany lots of holiday home owners etc.).
OT: No sure why everybody is so obsessed with the travel time from SEN to central London. The train to central London from STN is approx. 5 minutes quicker and that time is easily made up by not having to use a people mover and take an extended walk to the station, queue at immigration/security etc.