This is a red sport (mutation) of Alkmene, and noticeably redder and less Cox-like in appearance than Alkmene, although the characteristic Cox russet striping can be faintly discerned. It is grown commercially on a small-scale in the UK.
Alkmene is sometimes known as Early Windsor, hence the name of this redder sport, Red Windsor. However to further confuse matters, the marketing organisation behind this variety organised a UK-wide schools competition to come up with a new name - and "Sweet Lilibet" was chosen. This is therefore the name you are most likely to see it under in supermarkets, where it appears towards the end of September.