I believe that this excessive freight is because many UK companies are too lazy to go to the Post office.
I believe that DHL pick up from the seller so they like to use them to save themselves time.
The freight by Royal Mail for a 1KG package is GBP 15.28
Business Airmail | Royal Mail Ltd
So there it is. I have in the past specified Royal Mail shipment and it has been done but who knows now.
However for heavy stuff DHL seems OK as from LRDirect I noted that the steering box freight was up to AFAIR 50Kgs, so I added in some brake hoses etc. This is as long as the DHL do not try to add the $47 for AQIS inspection.
Regards Philip A