The BBC says the release "is part of a trial" and that a complete 4K library is still a way off. That will, of course, disappoint those who have already upgraded their TV. The challenge for the BBC is trickier, however, than Netflix or Amazon because it's also preparing for live 4K broadcasts. Conventional HDR standards would require an additional channel and wasted broadcast bandwidth; to solve the problem, the BBC has been working on a new kind of HDR called Hybrid Log Gamma (HLG) with Japanese broadcaster NHK. It's designed for live TV and is backwards compatible — so both HDR and "SDR" sets can read the same signal.

Little HLG content exists, however many TV manufacturers are already supporting the standard. The BBC has provided a list of almost 400 TVs that will support the 4K stream; they include sets by Panasonic, LG, Phillips, Hisense, Sony and Roku. The broadcaster says "the vast majority" of these will support HLG too, providing better detail in the shadows and brighter, more natural highlights and reflections. The nature of the HLG signal means that 4K, SDR TVs will also benefit from a "high quality 'compatible' picture" that uses the BT.2020 wide colour gamut.

"Blue Planet II is the first programme we've shown in such high quality and perfectly demonstrates how the BBC is pushing the boundaries of digital innovation," Matthew Postgate, chief technology and product officer for the BBC's design and engineering team said. I watched the final episode in 4K and HDR at the Soho Screening Rooms in London. It was, unsurprisingly, a stunning watch, with breathtaking colors and clarity. If you live in the UK and have a compatible set, I highly recommend watching an episode or two this Christmas, even if you've already seen the series.