Best answer by Gregor
Unfortunately some of the versions of Iphone 11 has been delayed since Apple themselves did not expect such a demand on pre-orders and after launch purchases. They are trying to meet these demands as soon as they can but certain versions will need some time to arrive to retailers warehouses. I have checked online out of curiosity and some of the storage versions are on 21 days shipping windows in most of the shops, like o2 and EE have 64GB version on delayed shipping. Currently there are some versions of Black, Red, White and Yellow available to be shipped instantly.
Sorry I could not help you more, some of the aspects of stock are out of retailers hands.