I complained earlier about receiving compensation for a cancelled train in the form of £25 Rail Travel Vouchers rather than a more fungible means of exchange, but they’re not as useless as you might think, at least if you live in London: you can turn them into Oyster credit.

I successfully did this at an Overground station. I don’t know whether that’s significant: Overground stations are part of National Rail, despite their TfL branding (hence why the measurements are railway Imperial rather than Underground metric, among other little details); whether you can do the same at an Underground station I can’t say.