[seabass-labrax]

It is mostly the same in the UK too, at least in principle. Sparpreis fares correspond to Advance tickets, which can vary over time or be sold at a discount. DB's Flexpreis would be called 'walk-up' fares in Britain, which are fixed in price by the Department for Transport (a part of the British government).

If you miss a train due to no fault of your own you can take the next available one, including with an Advance ticket[1].

What complicates the matter greatly in the United Kingdom is the semi-privatized franchising system and the hundreds of 'restriction codes' that limit the validity of the tickets to what is essentially an arbitrary subset of the available services, even in the case of disruption.

I think that German regulations, as well as European industry agreements such as CIV, are better for the passenger because they codify in law how reasonable railway staff would act anyway. However there are equivalent protections in Britain, albeit ones encoded in nebulous contracts and precedent rather than enshrined in law. They can help you but only if you know what they are and are prepared to fight the bueorocracy to invoke them.

[1]: https://www.nationalrail.co.uk/tickets-railcards-and-offers/...