Is it illegal NOT to save someone from dying?

[pmbuzz]

If you ignored someone just about to throw themself from a high bridge ?
If you saw someone drowning and just walked on by ?
If you encountered people in a burning building and just carried on your way?

Say you started to save someone by giving mouth to mouth or cardiac compressions but gave up, could you be arrested ?

 

[pmbuzz]

So, is NOT ringing the services an inaction that could cause death ?