The UK hasn't produced enough gas in the North Sea to actually run the country for a very long time, maybe ever. Anybody who sells you a dream about British gas for British people isn't telling you the truth and it doesn't matter whether they are lying or incompetent, you can't trust anything they say.

America, Russia and a handful of other places could do this. It's probably a terrible idea, but it is technically possible. However Britain is not one of those places.