Can an energy supplier retrospectively apply a rate increase

[Funk]

Received a letter today from my gas supplier (SWALEC) who have announced they're upping my gas price, from the 1st December! Given that we're now 3 weeks into the month, can they legally do this? Are they not obliged to give advance notice? What's to stop them deciding they want to backdate the increase to, say, January?

Be interested to know what people are paying as well. I pay 7.60p per kWh for the first 625kWh, and 3.31p for every kWh thereafter (prices inc. VAT @5%). It was 5.17p pkWh for the first 625 and 2.97p pkWh thereafter, so the hike's quite significant on the first 625kWh.

[Flat_Steve]

You are in fact allowed to write to your provider rejecting their price increase, you then have a certain period to switch to a new provider during which they can only charge you the current tarriff. Can't remember where I read/saw it but it was very recently and fresh in my memory.