..... Can anyone inform me which of these platforms were dedicated to certain routes.....
The National Library of Scotland's 25-inch-to-the-mile Ordnance Survey maps from the first quarter of the 20th Century suggest that the lines towards Liverpool were only ever served by platforms 1 to 3 on account of the sharp curve away to the south.
It seems like four running tracks went from Chapel St station to St Lukes, which would be used by trains towards Wigan, Ormskirk (via Burscough), Preston (via Hesketh Bank), the electric shuttle to Crossens and - until 1938 -
Altcar Bob.
This website:
http://heskethbankcouncil.uk/media-gallery/west-lancashire-railway/
shows a photograph titled "A Preston train leaves Southport platform 7 in 1964 hauled by a ‘Black Five’ engine....."
I hesitate to paste this interesting image here, as I'm unsure about copyright, but the photo is about 2/3 of the way down the page.
In expanded view it shows third rail installed on the northern pair of tracks to St Lukes, in line with
@Pyreneenguy's post regarding electrification of platforms 9, 10 & 11.
Also interesting on the left of the picture is one electrified track coming across from platform 3. This would be used by electric trains from the Liverpool platforms to/from the EMU depot at Meols Cop - which closed in 1970, half a dozen years after closure of the Crossens service.