Take a trip to Marylebone station and you'll find a mainline terminus with a bit of bike parking inside, beyond the barrier line (50-odd spaces on Platform 3) but absolutely none outside.
Signs warn you sternly not to park your bike on the railings. Many of the signs are easy to miss, though, because they're hidden behind bikes.
The consequences are predictable: railings, lampposts, benches - anything is pressed into service as impromptu parking, whatever the signs say, with sometimes unfortunate results (below right).
If you see other examples of this sort of thing - that is, badly parked bikes collapsed onto perfectly legally parked cars, causing possible damage to the paintwork - remember to do the decent thing: take a picture of it and upload it to Twitter, so everyone can have a look.
Chiltern Railways run from here to places such as Birmingham, High Wycombe, Aylesbury, Stratford and ahh... Bicester! Bikes go free and don't need to be reserved, but aren't allowed on rush hour services. Wrexham and Shropshire Railways are a new small company providing services to Wrexham, with some cheap deals; their bike policy seems undecided yet, and they say they allow bikes for a small charge on certain services but not in peak hours.
Monopoly's Marylebone Station costs £200. What could this buy you there? Assuming Wrexham and Shropshire do allow you to bikes on the services you want, you could book five normal-price returns (not advance tickets or special offers) to Telford. From there your party could spend a very pleasant day or two going down the Silkin Way to Ironbridge and exploring the Severn.