From the October 2016 onwards version of the National Rail Conditions of travel, page 21, available at http://www.nationalrail.co.uk/Conditions of Travel 2016.pdf
28. What happens when things go wrong?
28.1 If disruption prevents you from completing the journey shown on your Ticket, any Train Company will, where it reasonably can, provide you with
alternative means of travel to your destination, or if necessary provide
overnight accommodation for you
I suspect they may answer that a major weather incident means they can claim it isn't reasonable for them to offer a hotel, but I'm not sure what would happen if you challenged that hard afterwards...