Toilets aren't a legal requirement on train journeys (under a certain length?). Not every train has a toilet.
But expectations are very important. If I know no facilities are provided on the train, I will use them somewhere before boarding, and will let a train go if necessary to do so. If they are supposed to be provided, I might not, as I expect they *will* be provided.
If a train has a facility - any facility, be that toilets, aircon, trolley service, whatever - I expect it will be provided as advertised, and not flippantly shrugged off as "a luxury". If it isn't provided, I want a sincere apology and steps to be taken to remedy the reason it wasn't provided, not an arrogant and flippant brush-off like that.
The correct response from customer services there would be along the lines of "We are really sorry the toilet was not provided on this service, this is because it was out of order because of a plumbing fault, which is scheduled to be repaired on 18/12/16 as we are waiting for a part on order to repair it. Unfortunately due to a lack of rolling stock we have to put it out in service as the fault does not make the train unsafe to operate, and the only other option would have been to cancel the train".
With a proper incident management system you'd know the detail above to respond, it shows a proper investigation of the customer's issues, it isn't arrogant, it's apologetic etc. It's not ideal, but people recognise that Northern's situation isn't ideal at least until the new stock arrives. But the response they did give is "we don't care".
FWIW, I would expect *as a minimum* that any train with no bog has this highlighted on the PIS so a passenger can make an educated decision whether to board or not, and furthermore that any Advance tickets should be automatically valid for the previous or next train of that TOC if the passenger so chooses. GWR seem good at the PIS angle (ha!), others much less so.
--- old post above --- --- new post below ---
As for TOCs who use the excuse of the bogs getting full - proper prior planning etc. It's like mucky windows - schedule your trains to be cleaned and pay enough staff to do so. No excuse. You rarely see a mucky LM Desiro, so it's easily done.