It really depends on the route.
I don't know about now, but one of the longest non-toilet journeys used to be on the 313-operated North London Line from Richmond to North Woolwich - it was something like 70 mins for an end-to-end journey. But it wasn't a problem... as only rail enthusiasts would make the end-to-end journey.
Guildford to London Waterloo via Leatherhead has no loos and that service takes 74 minutes. It's 63 minutes to Clapham Junction alone!
Via Cobham it is still 64 minutes to London Waterloo. To Clapham Junction that is 52 minutes. The Clapham Junction times matter more because during peak rush hour there are no fast services to Clapham Junction, so effectively no services to Clapham Junction with loos. Reverse is true in the evening peak.
In fact not even all the slow services from Guildford stop there either. So if you got out at say Cobham, you could have an hours wait for the next service, or you have to change additionally at Surbiton.
As someone who uses the loo more frequently for medical reasons I'd prefer toilets on all trains. My worst nightmare would be a failed train for 4 hours or more. I would probably be in discussions with the guard or driver by the 4 hour mark!
I have heard station announcements about loos not working but equally I've been on trains where the first I knew was when I could find no working toilet.
Lately the toilets at Surbiton on platforms 3 and 4 are out of use during roof repairs but no notices up to say so. I didn't bother to raise it this time. I thought it won't be for too long a d they are working on platform 1 and 2.
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