Can suppliers put up prices without telling me?

No, they have to tell you if they are increasing their prices. You must be told 'within' 10 days of the date of the price rise, which means up to ten days before or after that date.

Click to switch:

Energy

But you also have to be told that you have the right to change to another supplier. You have 14 days after being told about the rise to tell them you are going to end the contract. If you do this, your supplier can't apply the price rise to you.  (Note: if you tell them you are changing supplier but then don't, the price rise will eventually catch up with you!)

Note: The 14 days does not mean you have to change to a new supplier in that time - it will always take a few weeks to switch. It just means that within 14 days you've got to tell your supplier you intend to change.

This is contained in the suppliers' Licence Condition 44, paragraph 6.