[bloak]

In some, but very few circumstances. In particular, I don't think the railway operator example works in the UK, at least not automatically, because, otherwise, why would they have special legislation relating to "penalty fares"? Look for the legislation on http://www.legislation.gov.uk/ if you're interested.

Here's an illustrative example that may or may not accurately correspond to the current state of the law in any particular jurisdiction, but it show why this implied contract stuff doesn't work in practice.

A farmer might put up a big notice saying: "By camping overnight on this field you agree to pay me £100 per vehicle per night." Then a bunch of travellers might camp there. Can the farmer sue the travellers for the £100 per vehicle per night? My guess is that he could only sue them for damaging his grass, because, despite what the notice said, the travellers didn't "agree"; they camped illegally and without permission, like they usually do. Probably they smashed up the notice to show what they thought of it. Therefore the farmer can only sue them for trespassing, not for breach of contract. (He might also sue them for the cost of replacing the notice if they did smash it up!)

Likewise, you could put a notice on the front door and every window of your house saying that by breaking into the house burglars agree to pay you X pounds. Would it help you in any way? Of course it wouldn't. You'd get laughed out of court if you tried it.