Not sure if this is actually connected to your DHL pricing, but there is a surprising amount of cheap air transit to the UK because it is a major transport hub. Fresh flowers and cut vegetables are flown to the UK from Kenya, simply because there is enough spare capacity (there are planes that would otherwise fly empty from Kenya->UK) that the air freight is very cheap. These 'backloads' as they are called are more common to the UK because, being a transport hub, empty planes are more likely to fly to the UK to collect another load to carry.

It also complicates things like calculating the carbon footprint of goods. Do fresh flowers from Kenya have a high carbon footprint, given that the plane that carried them would have flown there regardless of whether or not it carried the flowers?