quick air travel question (x-posted)

[happycycling]

I'm heading to the UK for a masters degree around September 18 and have no idea when I'll be coming back to the States. Round-trip flights are cheaper than one-ways (at least for the airline/airports I'm looking at), and the UK -> US -> UK fare is a better deal than the reverse for the same dates and airports. Would I get in trouble with the government of either country if I book the UK -> US -> UK flight and only use the US -> UK portion?

(I hope this makes sense.)