I've spent the night on a platform in Oxford train station on several occasions when catching the last train from London to Maidenhead and sleeping past my stop because ... well, you get the last train because that's just after when the pubs kick you out. It's a fairly comfortable train station to sleep in until the milk train to get you home wakes you up and your hangover reminds you it's too early to be moving but too cold for you to stay where you are. Reading and Didcot also fall into this grouping.
Cambridge, however, wasn't on my train line.