Well it is not just rent default.
Basically anything that breached the tenancy agreement. I.e pets, children, overnight guests. Whatever is stipulated really.
Regarding contracts, then these must be honoured providing there are no breaches.
As a general rule of thumb (although it is a legal mindfield) after contract the landlord has to give notice which is equilvent to the rent frequency.
That is you pay one month at a time, they have to give one months notice etc.
You can always squat, after your time is up. Unless the owners want to live in their themselves, you will have to be evicted via a court order. And this will be charged to the landlord NOT you. Further, it is not a criminal offence.