The shorter side, facing the 'Western' platform is the one designated the platform number. However, on numerous occasions the side facing platform 2 is used for 4-car formations, but drivers are advised when they're being signalled into the bay under those circumstances.Grantham?
It was built for cross-platform transfers to the Taunton line.Yeovil Pen Mill between platforms 1 and 2. However the doors are never opened for the platform 2 side and AFAIA that platform face has no advertised service.
Yesterday I took 12:10 Carlisle to Barrow first time using this service. When train arrived in P2 some passengers were waiting each side.Carlisle has been mentioned, specifically platform 2.
Door release is usually given on the side closest to platform 3 and this is where passengers wait to board but it was fairly common for conductors to release the doors on the side closest to platform 1 at busy times when it was desirable to prevent large numbers attempting to board immediately.
An example in the past was the old 1717ish arrival/1727 departure. On arrival there would already be a large number waiting and a large number wishing to get off. The train arrived as 2x153 and was booked to split and leave a 153 behind in the bay. Releasing the doors often resulted in passengers immediately boarding and then being unhappy after locating a seat at being told that unit was being detached.
Many conductors would release on the P1 side, allow everyone to alight, close the doors for the units to uncouple and then the doors would be released on the P3 side to allow the new passengers to board.