I watched Powerpuff girls regularly on Channel 5. They played the original US versions. If they DID dub it, they still used American accents, cause those accents were all I heard when watching it. Its unlikely they would spend money to reduce the voices with no accent changes, as Channel 5 is commonly known as a cheap Channel, a running joke in the UK.
I'm fairly convinced that a UK dub of PowerPoint girls never existed, and that the rumour would likely have spread from someone asking if the release was dubbed because of its placement on a UK station that someone confirmed as a joke.