Pearl Mackie is set to make her debut as Peter Capaldi’s sidekick on Doctor Who this Saturday, but to the dismay of some Whovians she failed to remember one simple Tardis fact during an appearance on The One Show last night.

Presenter Angela Scanlon asked Mackie – who plays Bill Potts – what powers the Tardis engine, to which the actress replied: "It's space engine oil… None of that congestion charge or pollution either. It's all good!" 

But no. It wasn’t all good because it’s actually Artron energy that fuels the Tardis – a mysterious element containing psychic traces that feed off the rift in space and time. Duh. 

The very moment Mackie forgot about Artron energy

Many fans took to Twitter to correct Mackie...

The actress can’t shoulder all the blame though, seeing as she was encouraged not to watch any previous Doctor Who series by showrunner Steven Moffat. If you're ordered not to do your homework, you're never going to pass the exam... 

Doctor Who begins on Saturday 15 April at 7.20pm on BBC1