"Graham J" wrote in message
...

I'd be interested in knowing the answer to this too. If there isn't a
good reason for this not to happen would this also mean there was never a
good reason for the two bay platforms at Dalston Junction?

To run the whole service reliably (and it's designed for up to 18 or even 20
tph ultimately) with adequate turnround times and margins you'd need a four
platform station at Highbury, and there isn't room.

Paul S