Here is a tweet from SWR in response to someone else asking about them. Apologies, I struggle with the new(ish) way of quoting on the forum so here is an image (with description for visually impaired members)
Image shows a Twitter conversation in which the verified SWR_Help account confirms withdrawal of 456s from Monday and quotes from the Train Service Manager that 456s were due off lease in February anyway and this has been brought forward.
I notice they say “off-lease” which contradicts what some reputable members in the know have said here about them being stopped but not withdrawn/off-leased. Having seen an earlier tweet in which SWR erroneously told a customer the North Downs Day Ranger is only valid on GWR - this is false - I would not be inclined to take everything that the Twitter team say too seriously.
Fleet list: I will begin working on an updated fleet status list and will post it on Monday to coincide with the 456’s withdrawal from service.