No, we aren't covered by such legislation in the UK, and there is no such thing as a "Good Samaritan's Act"
That said, as long as you act in the patient's best interests, respect their beliefs, gained appropriate consent AND acting within the realms of your training then you won't face procecution (this has been proven in law).
So, if you are a trained first aider and decide to perform an emergency tracheostomy with a pen knife and a biro you can fall foul of the law.