Is the BBC's Nick Robinson calling Gordon Brown a liar

The BBC's Nick Robinson in his piece today on the calling of the general election writes:

'Image Two: Alistair Darling emerging from the famous black door at Gordon Brown's side. The chancellor the prime minister planned to sack is now seen as a key electoral asset.'

Hold on a moment, didn't Gordon Brown flatly deny that he was ever planning to sack Alistair Darling? Here's the video...
So was Gordon Brown lying at that press conference or is Nick Robinson misleading the public now? It surely has to be one or the other...