(26 Sep 2015, 1:33 pm)GX03 SVC wrote Nexus and DBTW have access rights for 6tph in both directions, these have priority over any other service.
As the Northern service will already be near or in the 'block', it's easier to hold the Metro at Pelaw for the Northern service to pass.
Whilst that is true in a number of cases, I have been on a Northern Rail that has had to hold back, due to a Metro in front.
It makes sense to let the Northern through, seeing as it is an 'express', but it won't always happen like that.