It's been reported that there were approximately 40,000 Wii U systems sold during the console's launch weekend in the UK, making it near enough a sellout.
It was initially suggested that Nintendo would only allow 25,000 unitsu to be sold during the UK launch, but this was raised to just above 40,000. Outside of the initial shipment, it's been stated that stock is only expected to trickle" in for the remainder of the year.
This seems to be a popular strategy for Nintendo, as previous consoles have also struggled to meet demand. Analysts have suggested that had Nintendo made more consoles available for launch, they probably would have sold more. However, this would lead to less talk of the console being a sellout, and would create less demand for the platform.
Aside from the 40,000 console sales, it's estimated that there is a software attachment rate of more than 2 games per system and that's without taking consideration any purchases from Nintendo's Wii U eShop.