Best answer by stephenrand
Yes, you can switch from Pure Planet without penalty.
The question is, can you get a better deal? A comparison site will give you an idea, but make sure you actually compare what the rates are for gas and electricity with what you are paying now - and bear in mind Pure Planet's 100% green credentials, and their promise that their prices can go down as well as up.
Good luck with the calculations!
And bear in mind that if you are paying more than you expected, then almost certainly you are using more energy than you expected.