Various maps, for example
https://maps.nls.uk/view/114645498 have a siding against the platform marked as "C.R."; this could stand for "Carriage Road" either where road carriages were loaded onto flat wagons, or where railway carriages were placed for cleaning in between use on services. Might have been used for mail as well?
Here's a view of it from 2008:
The Railway towards Great Coates
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David Wright and licensed for reuse under this
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(Click on the photo to go to the larger original.)