Manchester SONEX/DESIG SID from 23L/R corner cutting.
 

Almost without exception and regardless of type or time of day, A/C on said SID's are turning to SONEX/DESIG practically on the climb out.
Any flight crew out there to please elucidate? Thanks in advance of an early turn? ;)

It's down to Scottish Control, they usually give a heading of somewhere in the region of East passing 4000ish feet when we check in with them. It probably keeps aeroplanes out of the way of any arrivals inbound from MIRSI or ROSUN.

Wot he said ^ !

After 4000' you're out of noise restrictions so a direct turn towards the east keeps you away from inbound tracks as described...but also shaves quite a lot of miles off the SID track. The cumulative fuel savings over a year (plus the associated reduced CO2/NO emissions) must be massive.