The Southern Railway Company has commissioned new trains on the Portsmouth to Brighton line that have no onboard toilets.
http://www.bbc.co.uk/news/uk-england-11358844
They say this is because the carriages are designed to maximise space available to passengers, but, tbh, I suspect a lot of passengers (particularly the Elderly, those with kids or the disabled) would prefer the toilets back.
The journey is 1.5 hours. I personally think that *any* company selling journeys likely to be that long should be required to provided adequate toilet facilities.