Since looking for a new job, I have realised my contract requires me to hand in a three months notice! This is just not feasible as I am not exactly high up! And every recruitment company also thinks this is quite steep! I am obviously not going to work the three months notice period... what are the implications?
Exactly as Zac says.
Three months notice is invaluable protection when working for a smaller company - in case the worst scenario happens.
Whilst you can't guarantee to be released, you can probably negotiate it down.
The implications of not giving the full notice period are theoretically you could be sued for breach of contract. It doesn't happen very often that an employer sues an employee in this way.