One of the problems I think is that the different TOC control's initial reaction is to go for the standard alternative routes from their book of problem solving.
So you end up with the apparently contradictory suggestions on the national rail disruptions page, where XC (possibly from a Midlands perspective - see below) are saying use LM and VWC to Euston then onward by SWT, which is probably their standard response to problems in the Reading area.
Now if SWT just see it initially as a problem with their trains from Waterloo getting past Basingstoke, one of their standard solutions is to advise passengers to use FGW and XC - so that comes up on National Rail as well - and there's the confusion. Someone touched on this in one of the other threads about this incident.
Also, on a normal Weekday or Saturday morning, 8 (possibly 9) units leave Eastleigh for various origins including all the early starters from Reading, Southampton, Bournemouth, and of course Guildford. If most of them were delayed for ages south of Basingstoke, there'd be knock on problems as far as Manchester by the end of the morning - which means using LM and VWC remained sensible advice.
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So, hypothetically as it doesn't seemto have happened, Readimg, Guildford, Havant, Fareham, but what then? Direct to Spouthampton, or via Eastleigth with a reversal?
As
Oracle says, when it is planned it is via Netley. Of course, if a XC service arrived at Fareham at some random time and the normal service was already running, I expect it would depend on exactly when in the hour it happened to show up.
If the train just in front approaching Fareham was the SWT all stations stopper, it might make more sense to run via Botley and Eastleigh and reverse - and as I pointed out earlier they have normal route knowledge for this from the Guildford ECS...