I’m curious what the official position is here. SWR tweeted today that if you feel unwell you shouldn’t board and wait for a later train. I asked if the guard would endorse an Advance ticket (assuming the SWR leg was a +connections part). They responded that they would so you could travel on a later train. I’m suspicious of something so customer friendly (if you were travelling from an unstaffed station they would have no way of verifying this) so I’m wondering if this policy is documented anywhere.