Your agreement might end on that day, but I am sure your provider will offer a similar dual fuel tariff. Mine did, and it wasn't as shocking massive increase that I thought it might have been.
All the companies are trying to get new subscribers, and are making offers that seem good, even offering a three year contract instead of the present two years. But if you look at all the details, you will most likely see there is no or very little difference between companies. Now thats called competition!.